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ROUGH DRAFT Art Rosenberg 2/7/67 Introduction

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1. This will be done at System Generation time or when the foreground task is initiated oe te will be an Operator function to abort d checkpoint any Tower priority fob in order So to satisfy the resource allocation needs GF a newly activated foreground task this does not apply to core memory Foreground tasks will not be normally timed out for execution but will run until Complee or waiting for I O As a special service for debugging parts of a foreground operation a quantum time EE may be requested such that if the task has not returned to the monitor within a given period of time it will be suspended as an error condition The foreground tasks associated interrupt will be disarmed It will be required that such foreground task be in the Slave mode at least that part which is being checked H oRER a out and that the monitor be called prior to execution to set the timer In effect it will be cveated as a user program with additional privileges of dedicated resources Every foreground task is considered to be an independent job with its own context requirements tempStack etc For economic reasons it is appropriate to organize resident foreground tasks to appear to the monitor as one job sharing a common temp stack This is possible because of the first in last out order of absolute priority Ualess so organized independent foreground tasks will require independent job associated storage In the UTS and
2. two or more terminals to Es under controlled circumstances For both of the First two services above it is necessary to have the addressed terminal indicate acceptance of a message or linkage Thus each such terminal must alert the system via an Executive Command ENABLE that it is ready tox receipt of messages or linkage If a terminal is not active it will be turned on by the yote if a direct internal communication line for the duration of the output Addvesstnes of terminals is by Bind number the system s user identification can be used to locate the proper SEEE number by querying the UTS Executive as to the whereabouts or existance of an Jotie user No remote dial up if such hardware exists will be performed for DIAL or LINK remote users must be active in the system If during the course of a linked operation a remote user disconnects the linkage will be automatical unlinked by the UTS system DIAL Service user may send a message of a fixed maximum length to any single console other than his own nae ie active and enabled indicated acceptance of miceespeay Carriage Returns within the message may be used since the New Line e decta placed in the text instead a echoed back The end of the message text is indicated by a New Line character See Meat P 40 The receiver s terminal will not receive the message if it is in the process of input or output At the first opportunity where either has just been complete
3. Active non core resident foreground programs N o gt n A o e Overlay elements for active user programs active load modules This storage is a critical resource for the UTS system and is a limiting factor on system performance and loading It must be kept relatively unclogged by excessive transfer requests and priority for residency goes to the storage items listed above i PARS Liet 1S Browet P K AS OF Pos ED ro PENNS J ee ae Sree AL OS T F E ott i Ad j 4 Bogt P Ha ft A fe Lae wtf G9 Bet Se a SLIP hn VELI ee EG ZAD on oF mo telat eae Pa Tyke et RP DA pp AD TO OPTIA Patt SAIRON E AA er Mm 25 Permanent Random Access Storage This type of storage must be random access in nature but speed of accessibility ee need not be as great as the Active Random Access storage Bither high performmee fives TNE pied ee ie 4 l abi PRAD s or high expacity eae cai be used although the latter sy clara ed Residency in this storage includes the following i 1 Public apeariee programs subroutines 2 Private libraries user owned 3 Batch Jae awaiting execution Job Stack 4 User permanent input and output files Die cite hs 5 Symbiont buffering for I O peripherals 6 Accounting data 7 Save for Restart cueee point programs User data files for input or output to an activated program will not be moved to Active Storage unless explicitly called for by the program This is done Aror input files by a request for fi
4. characters for timing purposes The above functions require that the K D devices be serviced by a superset routine which has as a base the normal communication software Identification of a K D channel must be made dynamically since a remote station could be either a Teletype or K D A second level K D processor will be sroda as a system routine for servicing mechanical editing functions This routine will specifically provide for page turning and line rolling of a user program supplied text buffer Other text editing functions which change text content such as insertion deletions addition etc must be handled directly by the user process such as the UTS Text Editor The user process will also be required to maintain the buffer for text page turning or line rolling when the terminal s request requires a new buffer full end of buffer reached free or patron Tet User File Types In the UTS environment user files will be of several types which can contain ditferent forms of the same entity Specifically the following types of files can exist for a user program 1 User generated source symbolic code 2 Processor FORTRAN generated symbolic code 3 Binary object code load module 4 Save for restart executable code Clearly these file types can co exist and must be ideweieiabies The user cannot be expected to create dntque special names for each of these forms of a single program Provision must be made in th
5. amaa NE ee a 2 a aama an ROUGH DRAFT Art Rosenberg 2 7 67 Introduction The Sigma 7 computer has been designed be provide for maximum exploitation of computer E R However hardware facilities merely provide the environment for software systems which must reflect practical implementation of computer utili zation techniques To this end the Sigma 7 software provides the Universal Time Sharing UTS Monitor System which encompasses those facilities and services appro priate for general purpose multi programmed on line time shared operations As such the UTS Monitor extends the operating capability of the Sigma 7 from the Batch Processing mode to a more flexible and dynamic form of computer processing I CONCEPTS OF THE UNIVERSAL TIME SHARING MONITOR The UTS Monitor has been designed to provide multi programming services for on sine interactive user programs in addition to batch mode production jobs sym biont I O and critical real time processes To clarify the operational environments which the UTS Monitor is designed to service it is appropriate to define a number of terms which will be used in this manual Multiprogramming A technique for maximizing the efficient use of a computer system by overlapping computation with I O operations In particular where one processing job cannot provide maximum overlap other jobs are operated concurrently to achieve such system efficiency at a reasonable co
6. for other users The size of this conte space is variable depending on the user program s operating needs and it can expand dynamically during execution by linking the user s virtual memory pages The contents of the user s context area includes the following See Appendix Pead Map Image Task Control Blocks Data Gonen Blocks Program Status Doubleword Simulated Sense Switches Program status indicators Monitor set Temporary storage pointer Communication Echo table private version The context block information is selectively protected so that only the UTS _ Monitor can modify its contents However the user program can read the information therein those set by the user or Monitor at known locations or use the data for indirect addressing Furthermore changes can be made to conter block contents _ through Monitor service calls Hh CAL Tra ps Since user programs are prohibited from going directly to the Monitor sure memory area by the memory protection hardware of the Sigma 7 computer the CAL instruction provides the mechanism for user programs Monitor intercommunication By executing a CAL inuteuerions one of sixty four memory locations will be reached where control reverts to the Master mode XPSD and the user s service request is examined further Not all the CAL locations are used by the UTS Monitor and the available ones can be employed by user foreground programs for various privileged func
7. A program whieh is stopped externally for future continued operation will be saved for restart In effect it is a dump of the program and its operating environ ment A save for restart may be generated by an operatsi i by a MI ENA pELOnEty real time program It is assumed that the program will be resumed exactly as saved shere fone snonextornal 0 peripherelscan be involveduhich req uire prepositioning ive tine ste a atcirete OS AAS AVLA ft pba magnetic bape 3 i iene a Amt vapa sits Epema iris S f l Ra p aan pee 43 A save for restart pre emption by a high priority program in the UTS system jae _ accomplished by simple swapping to secondary swap storage Resumption of the Sroekane operation is automatically caused by the exit of the priority program Files are ae closed for the saved program since continuation of execution will take place relatively quickly I O transactions will be allowed to complete if they are in process On the other hand a program which is manually saved for restart will not neces sarily be expected to be continued for a while Shut down procedures will be necessary to preserve the environment indefinitely This means that open files must be closed current I O transactions completed and scratch storage saved not released A unique identification must be provided for future restart since it will not be a fresh copy oe the program The restart procedure will require
8. EN na ta X Note ok t REET Carey ee as PROS 56x Mut CELEASED Flee 22 Part of the efficiency in swapping chores will be derived from being judicious about what has to be swapped By being selective physical core Space can be made available with minimal overhead or with more practical pay off in scheduling operations User core space will not be released unless required for other users or if the user program action explicitly calls for a release function e g program termination Given that a scheduling decision requires physical core space to be made available to an inbound user process or an existing one the following logical selections for swapping will take place 1 If a resident user process is not operating but is awaiting execution in the current queue priority level it will not be swapped out before less appro priate user space has been exhausted 3 2 Appropriate user space for swapping is determined by selecting a user process which is not ready for execution and is awaiting a Monitor service or input i e suspended 3 Among all user processes in item 2 the choice of space to be made available Protected space non modifiable unique to a single user not a common is selected in the following order process or data area gt Protected space non modifiable common to several users but not currently required for execution I Unprotected space modifiable belonging to a
9. abort However provision is made for user recovery or end action whereby if expressly indicated a user supplied recovery routine will be given information con cerning the type of error detected and the user program s environment registers status double word at the time of error detection This capability is particularly useful for run time debugging It is possible to have user programs which are designed to operate in ce a production mode or conversational mode Similarly pvoduetton programs can be initiated gt from a job stack or on line from a user terminal In the first case the user program must be designed to determine its mode of operation from the type of control device used This is set by the UTS Monitor when it loads the program i e from an on line terminal or a control card file in the production stack In the former case however the user can also initiate a batch job from a remote terminal using the BATCH command which will set the mod to production not conversational The program designed for both types of use will organize its elements to respond interactively or process batch inputs and outputs this may be done by having two types of front ends User programs can also be designed through the bove medion to switch their mode of operation from conversational to production but not the reverse One should not confuse the choice of output media with the scheduling queue for a user s job Once a job has
10. been assigned to the Batch queue it cannot be communicated with by the user w although its status can be controlled as any other job in the stack If however Pyevunineds output is not desired at a low speed terminal the d tput ean be shunted toa secondary storage file magnetic tape high speed printer etc The job can still ga remain in one of the on line queues for input control purposes Tuteractive Processing The most significant extension of computer utilization which is accommodated by Sigma 7 and the Universal Time Sharing Monitor is in the area of Interactive Processing For this environment the UTS Monitor recognizes the more dynamic needs of interactive users as well as certain implicit priorities of their operations Interactive users impose an implicit priority upon a computer system by the simple fact that they are on line to the system In providing this direct access to the computer it is necessary to satisfy the user with a response time geared to a man machine dialogue Actually the interactive user can expect two levels of responsive ness Conversational When the interactive user makes simple data entries issues Control Response ate Commands or requests a simple computational process he expects a rapid acknowledgment of his input or in the last case a computa tional result On Line It is possible for the interactive user to initiate a long and in Computation volved comp
11. different subroutines to be resident and therefore only those administratively identified for public residency will be loaded into the public space Public Routine virtual space is selective depending upon installation needs At System Generation time a specific set of subroutines is permanently established in the public space These ti meyer be changed during system operation and any other subroutines from the system library will be loaded as a private copy in a user s program There is no demand swapping of public subroutines because of the impracticality of _ dynamically moving routines in virtual memory For these users who wish to wees the maximum amount of virtual memory space in their maps they may ask for all subroutines to be private copies and the public sub routine space in their map will be made available for private use This permits a user program which uses few public subroutines to gain more virtual memory than normally available 17 User Program Context The UTS Monitor is structured along the lines of distributed centralization That is although various data must be maintained by the Monitor for an individual user program such data is not centralized in Monitor ore Memory space Rather each user program will carry within its addressing space areas devoted to Hator C ntrolled data storage Thus when a user is not active in memory it is possible to Liberate a maximum amount of his physical core memory swapping
12. free formats and will minimize any unneces sary user input To this end an action routine to scan incoming characters and complete the printing of implicit portions of a Command input is used This feature will be dis abled if the user has informed the system that he is an expert In the expert mode only the minimal characters necessary for explicit command definition will be recog nized by the Executive Command processor The user can leave the expert mode at any time by informing the system that he wants a fill for his inputs The Executive Command processor can process input messages in both abbreviated or completed input form 32 The Executive mode for inputs is explicitly entered anytime the sign detected upon input Once in this mode it remains there until an Executive Command which will start executing the user s program is given the user mode will then automatically be entered To explicitly enter the user mode T character will be used This mode is illegal unless there is an deceuciae user program and any messages sent in this mode are rejected accordingly Identification of Input Requests Any gonveveatioual input will be logically terminated on the basis of a New Line character code Acknowledgement of message receipt would be simply the echo back of a New Line code and the physical Carriage Return with Line Feed movement of the console printer However it is essential to identify the source o
13. of paper tape reading The handler in paper tape mode will generate a Scop Reader XOFF code in response to an end of message control character or buffer full condition gnd a Start Reader code when an Input Request is made always Output The communications handler for output accepts characters stored in a user program output buffer of fixed length for the given output channel Char acters are converted to ASCII code from EBCDIC before transmission by the handler Illegal transmission characters such as EOT are detected and cause the program ta be stopmed Requests affecting communication lines must be explicitly made to the Executive for proper bookkeeping The user program calis for output with a buffer full of ehaeaceens in the program s virtual memory As the handler takes control the buffer is emptied into a Monitor buffer with conversion to ASCII Characters te transmitted for output until an internal end of message is detected DEL or the record count has been reached whichever comes first The buffer will be released 38 to the user program when empty making it available for reloading The user program will test the DCB to determine when the buffer is empty In this manner the user program may keep a steady output flow going at a maximum rate It will be held up as long as the buffers are full Carriage Return Standard Convention for UTS The standard physical message length for the UTS terminals will be a l
14. program or data areas for masked values Save a modified binary program The interactive Debug program will utilize both the Teletype Keyboard Printer or the Keyboard Display devices It will op rate under the UTS Monitor service for any privileged functions These include w Error recovery control User interrupt control I O service Change of protection for user program areas File changes replacing or saving a binary program file 49 Modifications to a user program or patching the program for Debug calls requires that the program protection map be set to ALL ACCESS Provision must be made for Master mode access to be andes for checkout out Executive or foreground functions Such access must be guarded so that only system programmers can use this facility at proper times e g Operator control over when such access is permitted privileged consoles passwords etc Editor Service The UTS system will provide a basic general text editor which will operate both in a batch mode and conversationally It is usable to create text files and itt link to language processors for conversational programming It will be reentrant for multi ple users Le i Ve R The text editor will provide the following services k Initialization of a new symbolic file via File Management service Modifying an existing text file insertion deletion replacement addition Line number referencing Line numb
15. suspended user process Sus wK N THE SchEDULEk pended will refer to most recently suspended e g having just been executed Popes TES Wee LISERS Oe SUCK A PEDES within the current queue cycle RS be GhAUE Tirs MAURES hig p40 usta Pet HE et EES peices e maps to be modified p pug uG THS A A RENAN TE E rts mee ANLE A use counter for process or data elements will be required for users sharing common elements based on load time information to satisfy retention of multi use elements Reentrant elements are appropriate for available space since saving is not required no full swap but only some bookkeeping is necessary However such bookkeeping will z l i 2 amp i s Ld i include map maintenance for users and Se e nirane element is moved it will cause many s 23 Since hardware facilities are not available to handle actual core modifi ations or references BOriware checking of such history will be a source of overhead for l i pe questionable pay off Swapping Seara e will be assigned only on fast random access storage It will consist of space for all active unique user elements and common processes reentrant or common data active In order to mai atatn efficient swapping transfers it is necessary to compromise the amount of selectivity in saving user process elements That is it may be more expedient to save large blocks of user elements than to pick out C Little piece
16. task will not be delayed by any UTS Monitor overhead or current service function for more than that amount of time After the foreground task starts execution it may be interrupted by porns oer functions i e I O interrupts which will only execute minimal bogkeapine tasks before returning control to the foreground task If the foreground task cannot tolerate any interruption from the Monitor it must be at a higher E E FO ae level than the I O and communications In such cases the amount of time required the foreground task frequency of interrupt within a response duty cycle process time for ok the task must be considered as additional system overhead to be subtracted from the afin On conversational duty cycle and will impose additional limits te the number of inter lt active users accommodated by the system If a foreground task uses any monitor service it must do so by a normal request CAL The priority of its interrupt level will be recognized by the monitor for queuing purposes Unless the foreground task interrupt has been ET to interfere with monitor bookkeeping operations by not permitting a safety disabling minimal of all interrupts of the monitor monitor service can always be requested at any time via the normal CAL All assignable system resources will be dedicated to a foreground task when it is active resident or not except for core memory when it is not a resident foreground
17. will determine if it has been linked or loaded by the user In the first case it must preserve the registers used for arguments and will control the exit of the program for returning to _ the calling program Return will be accomplished by the UTS Monitor providing the identity and the next program location of the calling program at the time of linking This information is given in the registers along with the parameters for communication data file on dise or in common core If the check reveals that the program has been directly loaded by the user input will be handled in the normal way and the normal exit i e return to the Monitor will take place This mode of program intercommunication will be used initially for UTS instead of the tasking service required for PL 1 Tasking may be implemented at some later time when the PL 1 language is supported under UTS Intervention and Error Recovery User programs which under the Batch system would normally be aborted because of lt an error will merely be suspended stopped if the process is an Intersctive one Control is given either to the user console control Executive Mode or to a recovery _ Toutine specified by the controlling process or the object program itself a t 1 34 If aae ene execution of the user s program an error occurs ahithis trapped by the system or the user intervenes with an Executive Command to stop execution and perform some Debug operation an ent
18. BPM environment there exists an accounting problem where foreground tasks cannot be properly charged for CPU time This occurs when such tasks service their own interrupts and do not allow for proper stopping the clock for the interrupted job or user If this time is significant and known by being static it may be accounted for administratively on a percentage basis i e every user job will have a percentage of its compute time deducted because of foreground interference Alternatively if foreground tasks are averiodieally initiated they should be required to clock themselves or allow the monitor to do so upon entry and exit This ee d 5 on differential can then be used to adjust the interrupted jobs accounting information
19. F Standard Run Time Package e g Fortran User Program Dynamic Area Service Subsystem e g Fortran IV User Dynamic Data Area User Dynamic Data Area sme ten ee fixed virtual memory locations in all users maps tzj n overlayable processes in virtual memory but resident in actual core memory 16 Certain functions are assigned to permanent physical locations Such functions are tiled to the hardware interrupts traps and because they are not relocated can operate without the map A dedicated foreground process can be so treated and avoid map sharing of virtual memory Physical core memory of course is still being shared _ Public Siuroutines ih sient eieane facility of the UTS System is the ability eorotavide useru sub routines reentrant e g mathematical routines byte string routines Eteri forceone current utilization by several user programs This feature minimizes core storage requirements in a shared memory environment as well as swapping overhead For Sigma 7 the public subroutine area is a dedicated portion of the virtual memory space This space is dedicated in each users map as is the Monitor space since program addressing within the public subroutines must remain constant Inasmuch as it is uncertain how much of this Ayub licit apace should be allocated for a given installation it becomes a System Generation varade ter Furthermore each installation may require
20. Mode depending upon its operating requirements This facility will require that any user supplied foreground task which operates in the Master Mode must be thoroughly checked out before it can be safely operated in the full UTS environment l Although the UTS Monitor will provide a maximum of generalized services and facili ties for real time operations it cannot by definition protect the user from himself Most specifically in a time shared environment it is quite tempting and easy to over load the system In attempting to operate several foreground tasks concurrently it is essential to provide sufficient system resources if proper responsiveness is to be maintained Peripheral Processing l One of the important facilities available and important to the Universal Time Sharing Monitor is the capability of performing concurrent bulk input output transfers _ between various peripheral devices particularly to and from disc storage with minimal interference to other computations To accomplish this two sopes of service functions are provided by the UTS Monitor Bi l SYMBIONTS _ COOPERATIVES In essence peripheral processing consists primarily of I O transfers with a small amount of computational effort to drive the peripheral devices Symbionts are the driving routines for peripheral processing and there can be input and output Sym bionts for every Sigma 7 I O device They operate on the basis of bulk transf
21. Only the originator terminal may Join or Unjoin other terminals or issue any Executive Commands which may affect the common program The only Executive Commands which a Joined terminal may exercise are the DIAL and QUIT commands Once a cerna has Quit or been Unjoined that braia reverts to normal usage When the Originator terminal terminates the gommon program all Joined terminais are released and turned off Joined terminals cannot link or be Linked to Inputs and outputs to and from each Joined terminal are not seen by the other terminals each has its own communication buffers in the common program Each terminal thus must be speciticaiiy addressed by the program The originating terminal is the only one implicitely addressed i e any input or output calls not naming the terminal channel number will refer to the Originator terminal Checkpoint and Save for Restart _ User programs which are in operation may be stopped and saved on secondary storage for resumed operation in the future This facility is operaba in two modes Check point and Save for Restart 42 Checkpoint Checkpoint is a mechanism for a long computational program Batch Mode to periodically snapshot all elements of its current operation so that the program need not be completely reinitiated because of a system hardware or software failure Every snapshot will include core memory contents and secondary storage files as well as fies program s environm
22. a Hom dere se cami Gs EN stg Om CY iha On ren 1 Performance The performance characteristics for the UTS system are l Monitor overhead for disc and core storage management scheduling accounting context switching I O control and Executive command processing will ot exceed 5 of the total operating time CPU of the system This includes over lay of Executive Funck Lons where necessary but does not include user requested 1 0 transfer time 47 Interactive communications processing character oriented will not exceed 5 of the total operating time of the systema nr CPU Swapping time will be masked by having enough user spaces in core memory such that one or more users executing their full conversational quantun will equal the time to make a swap of two other conversational processes The user space size is the size of a typical conversational process and or user context data The core residency for the UTS Monitor will not exceed 20 of the total minimum core space configuration This does not include user context storage A conversational process is an interactive process which will have a maximum response time of 3 seconds from the time of receipt of an end of message character to the start of the response output This response time gt is not guaranteed for a user interactive process which requires any I 0 service other than console I O and normal system swapping one swap The 3 second time interval i
23. able to determine if the input character is a control character is also made Control characters either indicate a change to characters already received backspace cancel a mode switch for the UTS Monitor Executive Command user program input or an end of message signal If a control character is found the appropriate action routine is activated i e move user buffer pointer select user or system input flag set message complete flag etc 37 The handler makes a conversion from ASCII code to EBCDIC unless the user s Se ieee ack wish conversion and places the character in the user s ked length input buffer Message assembly in the user s buffer continues until an end of message character is received or the buffer is full If the user s buffer is full a NAK character is generated to che console to 1oeke out further inputs and the user program input complete flag is set For end of message control characters the NAK output is optionally generated for locking the keyboard as per the echo table indi cations When the incoming character has been PEODE DEY Bipeeuecd the handler clears its interrupt level and exits Paper tape input is treated as keyboard input except that a rub out code DELETE is recognized as a character to be ignored Furthermore the Teletype requirements for remote paper tape input are that start and stop paper tape reader functions XON XOFF be provided This permits proper computer control
24. al cases or for an installation s environmental requirements 30 The UTS Monitor provides a Queue Seecus ndale which will be activated every time an interactive user srogram makes a service call to the Monitor or is trapped by che eye raii This module will determine by a parameterized decision table whether or not the user s queue status should be changed This decision is edtcen before any monitor service is rendered System Scheduling Above and beyond the scheduling control described above for user execution the _ UTS system services programs on an implicit scheduling priority This applies to all Monitor functions required by user programs That is services are rendered according to the following implicit priorities First Level l Real Time foreground tasks by interrupt level a Interrupt connected EEY b Resident or non resident in core 2 Synchronous Foreground tasks a Serviced by Monitor clock watching function Second Level Es Interactive Programs Conversational Mode 2 Interactive Programs On Line Compute Mode Third Level l Batch Jobs by explicit priority The second level interactive processing is broken down further into the fol lowing priorities for UTS servicing 3 1 Executive Command Processing 2 User Program Ready for interactive output 3 User Program Ready to execute and in core conversational mode 31 4 User Program Ready to execute and in core on line co
25. at is if a user program executes a service call to the Monitor the time will continue to be charged to the user until he is no longer executing or being serviced In addition to those items accounted for under the Batch Processing Monitor elapsed time must be recorded for terminal usage Core residency will not be recorded when the user s program or parts of his program are not required to be in core memory i e they are eligible to be swapped out Actual swapping costs are not chargeable _ to the user Uda fee 7 eae n 35 The UTS accounting package will provide recording of all chargeable resources on a summary count basis This data will optionally be dumped onto secondary storage according to System Generation parameters The reduction of such data is delegated to an optional user supplied process to produce an accounting report for adminis trative purposes The on line user will be able to retrieve current ecounrine data through a UTS information service command Start Up and Shut Down The UTS system operation will utilize a start up and shut down procedure for iterative use which maintains maximum operational continuity for on line system users The start up and shut down procedure will apply to a system which is going on or off the air completely or when scheduled interactive use begins and ends while other func tions e g batch and foreground may still operate At start up time all local terminals will be tur
26. batch mode o operation Such programs are available from secondary storage and are recognized in the UTS Executive command list Private programs re quire specific file management service for loading and operation Service subsystems i are often in high demand for convenient response to interactive usage and can at System Generation time be made permanent core residents However in general the Service Subsystems are Basic programs for system users which are treated as user pro grams when operating The following subsystems are currently available in the UTS system Symbol oE Meta Symbol FORTRAN IV Debug and High Efficiency SYMBUG DDT TE EDITOR HELP COBOL Batch mode only 1401 Simulator Batch mode only Other service subsystems can be added to the System at System Generation time to serve particular application needs of a Sigma 7 installation Such subsystems must be carefully administered as far as becoming public system services since they should be properly checked out documented and be appropriate for installation needs Other useful routines and programs can be made available to all users by being entered into a public library and loaded as a private program through the file management facility Map Sharing All programs and routines including the UTS Monitor which will be operating together in core memory must share a common virtual memory i e the same hardware map This affords maximu
27. ction throughput Once a production job in the background has been Saeed its allocated facilities 1 0 davies secondary storage will not be _preempted except by a foreground task or operator action Actual Monitor service for compute time and 1 0 operations will however be given to a batch job at the Lowest level of implicit priority unless compute time is explicitly dedicated for such operations At the Background level there does exist a second level of priority which is explicit Normally jobs can be entered into the stack with whatever adminietvative priority is appropriate However this will not cause a current Background job to be TN Operator action or a service call from a foreground process can cause a checkpoint of the current background job with draining of current I O operations so that an important Background job can be initiated as soon as possible In the worse case the current Background jov can be terminated abort immediately and veinitiated completely at a later point in time By definition Batch jobs are unattended operations As such run parameters must be provided to the UTS system which define maximum operating Limits which should not be exceeded if such limits are violated the job will be terminated Where such limit parameters are not provided by the user system limits are imposed by default Similarly in the event of system detected program errors the default case will bea job
28. d the message will be delivered with the sender s channel number appended to it If lt a terminal has not indicated message acceptance a DIAL command will be rejected A special case of the DIAL function is available to the Computer Operator s console whereby he may dial all active terminals for public notices of importance The operator s console is addressed by DIAL 0 OH and his terminal may be assigned to any terminal during system operation Terminal Linking Linking of several terminals is initiated by a logged in user whether or not a program is loaded or operating or not on that terminal linking can be initiated at any time Any Active linked terminal can cause a program to be loaded executed stopped or terminated Linked consoles can be made Passive or Active by the link originator gt that is they may either be received only for any program output or they may input and receive output as well All terminals may always issue Executive Comanda While any Active linked terminal is inputting in the User Mode to the program all other ACNE terminale cannot input to the program This is necessary to avoid confused input to the program input buffer All inputs from every linked terminal are seen by all the others as well as all outputs to any terminal As any terminal links a terminal to his or vice versa a message will be issued by the UTS system indicating who is linked to whom and the type of linka
29. dynamic scheduling of user jobs in the multi programmed environment of a time sharing system Based on user service needs and the load on the system the task scheduling function determines the operational behavior Be any given system Because such needs will vary from installation to tastat ation _the UTS system recognizes that the task scheduling logic must be highly flexible for 27 proper adjustment and tailoring Consequently the major scheduling elements have been made installation parameters which can be specified at System Generation time and or while the system is in operation The scheduling logic which can be so adjusted lies primarily in the area of interactive use Overall scheduling consists of three user areas i l Foreground real time 2 Interactive users 3 Background Batch jobs Foreground jobs are assigned priority in apesiuke rank order based on priority interrupts Synchronous foreground jobs have higher priority than interactive users and are activated when clock timer runs out The UTS Monitor does the clock watching The time allocation for foreground seeiieies should be preplanned by the user installa tion to insure against overloading the system The interactive user level is the area where great variations can occur and scheduling can be tuned accordingly Within this level are two types of operations 1 Conversational Processing 2 On Line Computation Dyna
30. e File Management facility to accommodate a file type ident ifier This identifier can be explicitly employed directly by a user or implicitly through a processor For kamp te if the user wishes his program to be loaded for execu tion it must be the binary object file If it is to be compiled it must be in the processor acceptable form If editing is required the user generated form is called for When files are modified or deleted again there must be some control for assuring lt across the board coordination For example when a user generated source file is up dated the processor formatted source file must likewise be changed el n Ronen Aiai A UTS oe gas The UTS Monitor will provide the same services to foreground tacks as specified for the Batch Processing Monitor However because the map hardware is available gt certain factors must be considered Foreground tasks both resident and non resident can be sreietencly operated in the non mapped mode Non resident foreground tasks are assumed to be tolerant in otis of response time and can afford to wait for physical core space to be made avail able and to be eelocaced to that space for execution If a non resident task is not tolerant it should be made resident Furthermore once a non resident task starts executing it should not be suspended swapped out and hen resumed Unless a foreground task requires the common use of public reentrant sub
31. e user s physical memory relative to the virtual space Thus a limited number of physical core memory pages can be used to service a larger number of virtual memory pages This approach will 24 _ afford a reasonable and practical method for efficient core space utilization without dangerous guessing and excessive system overhead In addition to the above method of reference loading explicit overlays can be IG called for by an erectie program This is an overlay in the virtual memory space and consequently in the physical space as well Auxiliary Storage Organization for UTS Auxiliary storage requirements for the UTS system are greater than for those of the Batch Processing Monitor for a number of reasons _ 1 UTS System is larger in size 2 Additional forms of storage required 3 Volume of storage requirements significant Auxiliary storage in the UTS environment is divided into three fundamental categories l Active random access storage 2 Permanent random access storage 3 Permanent external storage Active Random Access Storage This storage requires the SDS high performance rapid access disc for naximizine multiprogramming efficiency in the UTS system Contained in this storage are the fol lowing types of files l UTS Main Monitor and Executive Routines 2 System Bookkeeping data e g file management directions Service programs Swap storage for active programs Scratch storage for user prostans
32. ental context data registers DCB s etc The conditions for checkpointing can be based on time or at logical phases of the program s operation Successive snapshots of a program s operation will always replace the one last saved The checkpointed program will be contained in a permanent file identified by the user s account number and a unique user supplied file name not the name of the original program which has its own file name If the checkpointed program is to be activated it is run as a new job Furthermore salee explicitly preserved the checkpoint file is automatically deleted from permanent storage when it is executed An operating program can call for checkpointing itself directly by an Executive service call or it can have a run time routine which will respond to periodic time interrupts and call upon the checkpoint service At the time of checkpointing any on going I O operations will be completed and all I O status information preserved in the program s context area In restarting a _checkpointed program a restart routine location must be provided which will reinitiate all environmental conditions such as open files magnetic tape sofuittoning etc rie is assumed that the self checkpointing program maintains the proper restart informa tion for itself at all times The UTS Monitor will provide the proper communication to the Restart Module at load time to activate the re initiation information Save for Restart
33. entral bookkeeping functions i e a real time foreground process with dedicated facilities In only a few strategic areas will the interrupt problem be regularly forestalled by interrupt disabling while critical bookkeeping is performed that is pushing machine register contents se Privileged Functions In the UTS Monitor system all machine controls are considered to be privileged _to the Monitor and those real time tasks which require such privileges Thus a user program can normally only exercise a machine operation other than computation indirectly by akae ene Monitor to perform such a function This applies also to making changes to data located in Monitor controlled storage areas in a program s virtual memory This is necessary to minimize or eliminate any accidental catastrophic system hang up due to a software error By centralizing privileged operations as much as possible even within the Monitor OETA system maintenance extensibility and modularity is greatly enhanced Executive Functions Executive functions of the UTS Monitor are disieu ked from the more fundamental Monitor services by the fact that they involve the administrative tasks initialization or termination functions secondary operations for user program operations or non critical yet useful functions for system Guanes The Executive elements of the UTS Monitor do not themselves perform any privileged tasks directly but cause the main Monitor elemen
34. er the requirement for accommodating Batch operations in this manner is that core space for a Batch job must be pre allocated so that no swapping interference takes place The Batch job must be resident while it is active getting CPU time all during the duty cycle It may be removed only when its CPU time is exhausted however excea IS VERY EEFI ELIAS oo toa this ynot bassactdged m Verna A Thuau Vaa Shifting Between Conversation and On Line Compute Modes One of the difficulties encountered with interactive time sharing systems has f 4 been to differentiate between the conversational and on line computed phases of an interactive process Early systems simply used capaces time utilized as a measure of this differential However other clues can be employed effectively The following ground rules are follwed by the UTS system to determine the status of an interactive process 1 Any I O call for interactive input i e keyboard with a WAIT option will be considered as a sign that the program is indeed in a conversational phase Ce korido Raut Agus T O 2 Any I O Fequests except input or output to the interactive terminal will be considered as a sign that the program has shifted to an on line compute mode 3 When the time quantum for the conversational queue has been exceeded the program is dropped to the on line compute mode Needless to say such ground rules for scheduling can and should be modifiable to handle speci
35. er insertion using decimal system Line numbers will be provided by user E Automatic resequencing removing decimal point values upon user request List with or without line numbers Line numbers will Kot be Considered necessarily as part of the text 7 Rename a current symbolic file Merge symbolic files into one file Tab input lines by Filling with spaces according to software tab settings Provide in line editing character editing The Text Editor will be called by an Executive Command Further commands are processed by the Editor itself When operating in the Batch mode inputs are card images No interactive response is given for any input request If any error occurs with the input the error message is logged and the process will abort a 50 Editing and the SDS Keyboard Display Es The SDS Keyboard Display device has implicit siai reine for editis service above and beyond normal terminal input and output The first level handier functions for K D device are based upon the standard Sigma Shavadter ortented communications equipment with several differences a A different echo table is required since new control characters are re used pk Message mode capability of the K D requires identification of a message leading ETX character and no echo of the message characters Dynamic an switching of echo table pointer Output message generation requires control character buffering with NULL
36. er map will have the same virtual space dedicated to these public subroutines and or run time packages Thus by switching the map only the subroutine storage areas will have to be changed to reflect a new user s context location in TAI core memory This scheme will not permit dynamic storage to be used any subroutine requiring dynamic storage will have to be private copy inthe user s program A user program must indicate at load time whether or not the standard subroutine package s should be used or only private copies should be loaded 20 III UTS FUNCTIONS Core Memory Management The UTS system allocates core memory on a dynamic basis in order to support the multi programming environment It is required that sufficient core memory be avail avie during system operation to acond enough user processes so that program lt execution can take place while I O and swapping are being performed A System Generation parameter which can be overridden by the Operator during system operation is the maximum size of physical core memory which will normally be made available to a user program This is necessary in order to avoid having a particular user program Sc enaee system performance for other users If a larger pro gram and or data is required by a user a logical overlay at that program S ex pense will be performed Physical core memory areas will be allocated on a dynamic basis to all processes requiring such storage Ba
37. er terminal service Dial Link Dial up service from the computer JOIN service for multi user programs Character Oriented Communications Handler The fundamental software module for UTS communications service are the Character Oriented Communications Handlers They perform the following functions Input The normal status of all UTS terminals will be Active waiting for char acters unless the power is turned off or the station is disconnected remote Cy AtuTiVk MODE MESSAGES Will ALWAYS Be ACUESTED USER hoD MESSAGES Cie THE USERS PROGRAM WILL OMA BE ALdEPTEO WHEY TALE PROGAH REQUESTS ET On external interrupt the handler examines a common input table for new characters which have arrived since the last inspection The BOON input abie is designed as a data chained doubl buffer so that even if characters are not emptied from one half the other half can be used for further inputs It also causes character srGceeeins to be done at least at the critical point when one of the buffers is full if not earlier A pointer is maintained to indicate the word location where new unprocessed characters begin Each input word contains a single character and an identification number of LIME the user s tGheanwret The handler checks an echo table associated with the bal AE given ghana and generates an output character or no output according to the echo table indication for the input character A check using the echo t
38. ers _ independent of any user program needs To accommodate format needs of a user program the Cooperative routine is employed or to feed I O data to and from a Symbiont On input a Cooperative will break ea ithe data or the user program for output a Cooperative would pack the data for the _Symbiont Symbionts have an implicit priority higher than background production jobs but Lower than interactive or foreground taska Symbiont operations are initiated by Opera tor action and can be terminated by the Operator as well Symbionts are also auto matically activated for normal Batch job operations e g printer output via the disc User programs use Symbionts in conjunction with Cooperatives for interfacing as dows eribed above Multi Processing Several features of the Sigma 7 computer coupled with the UTS Monitor could be used for a multi processing environment The hardware map tasking service reentrant routines of the Monitor etc lend themselves to task oriented multi processing The UTS Monitor does not nide for multi processing however since additional extensions are required for this purpose etay in the scheduling logic to permit execution of more than one process at a time In addition control would have to be exercised over the bookkeeping tables of the Monitor such that only one CPU could modify common data at any given time Other complications would be caused by I O and external inte
39. ervice from other users Through the use of such parameters a system may allocate maximum amount of these resources special case privileged allocations or first come first serve unrestricted use of such resources Non sharable resources will be allocated on a first come first served basis and or by dedication to privileged foreground programs This will be done either by lt Specific assignment at System Generation time or upon user program demand 11 II UTS STRUCTURE The Universal Time Sharing Monitor encompasses all of the features of the Sigma 7 Batch Processing Monitor since a comprehensive time sharing environment includes pro duction job processing as a background operation As such the UTS Monitor is actually structured upon the functional elements of the Batch Processing Monitor with several notable extensions Core residency and overlay organization of the Monitor is different because of the more dynamic envionment for interactive users And addtetonal Execitiye services The Sigma 7 map facility is used to advantage wherever possible for dvaaaie relocatibility context switching core space management etc a Provision is made for automatic swapping between core memory aad fast disc storage to provide maximum computation and I O overlap Scheduling is provided for the multi user and multi task environment File management control is extended to cover the on line multi user operating environ
40. f the process which is acknowledging the input and requesting further input Thus in addition to any output messages which may be generated the UTS Executive Command processor will always start a new line followed by an to indicate to the user that Executive Command input is currently being expected and that the terminal is in the Executive E modes This approach will also be used by any public service program such as the basic Text Editor Debug Help etc where not only is the fact that input requested but what process is expecting it This is particularly useful when dealing with process to process linking and it may not be clear to the user which process is in control Calling Service Systems The Executive Command processor will recognize all requests for Executive action as defined in Appendix In addition it will recognize by name the user s request for a system service program to be loaded and initiated Executable Command Files and Program Calls to the Executive Command Processor The UTS system provides a flexible mechanism for allowing a user program to gen erate an executable file for system processing The user program can set up in symbolic text form the same commands that can be typed into the Executive Command procesor An Executive Command file reader then scans the input text executing each aer OA wear G Sf eful Coki p Lipe J The executable file may also be created by the user A and give
41. ge on both terminals A terminal or group of terminals may be linked to only one active user pro gram at a time A lLinkedtorminetmay tnlink aayofthe otherun inked terminels iomitselblic Any linked terminal may unlink by giving the UNLINK command to the UTS system at which a point a message to the remaining linked terminals and the unlinked one will confirm the Executive request It should be noted that each linked terminal is not independently in the Executive or User Mode according to the mode switch last used by a terminal the current mode is applicable to all linked terminals no matter which one set it 41 All linked terminals can conveniently converse directly without using the DIAL command All that is necessary is that each line of input be terminated with a Cancel character CAN which will be echoed with a New Line JOIN Function The JOIN function is exercised by an operating user program for a group operation vla input from the Originator console The Originator terminal which activated the program provides the program with the terminal BAERE diber which are to be used ta he Monitor service calls Active or Inactive terminals except Inactive Remote stations which would have to be dialed up can be joined Active stations must be enabled for the JOIN function and cannot have any program currently in operation Inactive stations may always be joined and the JOIN function starts up those terminals
42. ine of 72 characters not including the NEW LINE code The NEW LINE code will indicate a logical End of Message A Carriage Return code will be echoed pace meee a New Line code and will be considered as a text character at all CONVERTED times It will also be VE to a New Line code when detected in an output message text New Line codes will not be automatically generated by the Communications Out put Handler at the end of a message However an output character count will be cumulatively made and if 72 spacing characters graphics have been trans mitted without any New Line characters or carriage return a New Line code will be sent out if the 73rd character is not one Terminal Status Management An important part of the communications package deals with maintaining proper bookkeeping of each user terminal Each user software channel is activated when a connection is made by dial up or when power is turned on at a terminal JA mode flag indicates whether the user is currently talking to the Executive or a user pro gram This flag is changed by an input bonerol character and or automatically by a GO Executive Command User identification by name is kept for each channel for information purposes in using the interconsole communication services Input or output activity status is maintained to avoid conflict between inter console messages or Monitor messages and user program input or output Inter console link status a
43. le movement copy from Permanent Storage to Active scratch storage Output Piles tenaca by user poran Active scratch storage must be explicitly saved before termination in order for them to be preserved in the system Otherwise input and output files will be accessed by a user program directly from Permanent Storage System Generation parameters are used to define the allocation of all E T storage available in the system including maximum limits for individual users both Permanent and Active storage The allocation of Permanent and Active storage will have a more significant effect on UTS system configurations that have high speed discs and high capacity discs where only high speed discs are used movement from Permanent to Active storage will not be necessary Permanent External Storage Magnetic tape is required to backen randomsaccesg storage aa will be used for purge storage when Permanent Random Access storage becomes full or when permanent copies of programs or data are required Purging will be ander Computer Operator Zontrol in terms of selecting files to be purged Age of files when last used as well as priority will be taken into consideration geaoratee to installation administrative rules The UTS File Management system will provide inventory display of current files on Permanent wane es De i f i A ee ee ie Pa hehe 26 random storage and will purge to tape either eee files or files selected by age of use or ow
44. m operating efficiency under the hardware architecture of Sigma 7 Public functions must be consistently allocated the same virtual memory areas to allow for concurrent use by multiple users This means that a user s memory map 15 will include all public reentrant routines of the UTS system that are required for the user s operation and these routines will always be in the same virtual address locations For public library routines which are available to the user but not on a reentrant basis or for popular multi use any available virtual space is used at load time Map sharing should not be confused with the sharing of physical core memory Routines and or data used by a program may be in physical core memory but not neces sarily in the program s map Thus a program which uses overlays may have the overlay segments in core memory and the overlay action consists of simply changing the physical adeewses in the memory map Programs designed for Sigma machines without the map hardware and smaller core memories will be operable ina more efficient manner by using the map in UTS for virtual memory overlays Map assignments of virtyal memory will typically appear as follows sare omarion v F Monitor Area K F Monitor Area x i F Monitor Area User Context User Context o Context k F Gar Public F System Public ee Program Routine Area Routine Area i F Service Subsystem e g Editor OR
45. ment The accounting mechanism is extended for the on line multi user operating environment Management of public subroutine virtual memory space is provided for Dynamic core space aitteeaeian tg provided through the Sigma 7 map Provision is made for character oriented communications processing and inter active user console services 7 oA conversational Executive Control Language processor is added to siiepicniede the normal Batch Mode Control Card Interpreter The UTS Monitor occupies a portion of the total rewil memory space 128K avail able to each user This sharing of the map permits the UTS Monitor itself to take jds _ vantage of dynamic relocation for greater organizational flexibility It also enables more efficient Monitor interaction with a user s progran by providing a common virtual Memory reference between them at all times 12 The UTS Monitor is composed of a number of functional modules all of which are pure procedures and therefore reentrant Those processing modules which are not required to be permanently in core can therefore always be restored with a fresh Bene from disc instead of being saved each time The monitor processing modules are linked together by central communication and bookkeeping data tables Any Monitor process may be interrupted before completion and geanbered progiains the common bookkeeping tasks have been completed or if the interrupting task is independent of the c
46. mic parameters for conversational processing are l Maximum number of interactive users allowed in the system 2 Conversational time quantum maximum amount of time allowed for conversational mode Bi 3 Conversational duty cycle Parameters for on line computation are 1 Number of queue levels multi level queue 2 Time quantum for each level 28 Multi level queues ave functionally useful for the on line compute mode of interactive processing for several Jeaan First it is difficult to ascertain the length of compute time required to service this mode for all users in order to produce the response output Second since Gane must be equitably shared normally it is asevopeiace in the system to feel its way in a dynamic and uncertain environment l Finally it allows a finer categorization of interactive use ina generalized ER such as UTS e g large size processes may be immediately relegated to a lower priority 3 queue when in the on line compute mode The multi level scheme can be employed either as a fixed assignment Herhod for E known types of processes which is difficult without installation experience or as _has been done with several prototype time sharing systems programs can be pushed down to lower priority levels with accompanying longer time quanta as required dynamically The goal of such scheduling is to favor conversational response and fast short on line gt computation as opposed to longe
47. mon process are the same The requirement for reentrant process is that it be pure ape cedure never modifying any instructions only data Since it is difficult to verify whether a program has indeed been implemented for E EA when written in assembly language and since public service programs should be properly controlled the assumption will be made that a program is not reentrant unless administratively entered into the system The UTS system requires reentrancy for all programs and subroutines which will be public and used concurrently by multiple users By definition reentrant prones must be pure procedure nd modification of instructions and separation of process instructions and context data from data temporary storage and context on a page protected basis All reentrant programs will utilize the map to switch from user to user for a reentrant program Subroutines both for the standard System Public Subroutine area and for the standard Run time sadace for a language processor must be organized by the loader to have any local storage separated from the process into independent pages To accomplish this the standard subroutines must be organized into two blocks one block of M pages will have the processes instructions and constant data salyi the other block of ty pages will contain ait a6eal storage for the subroutines The loader will adjust all addresses in ee subroutines to access the relocated temporary storage Every us
48. mory This is essential for maximized efficiency in a time sharing environment where secondary storage disc is used for inactive program residency and swapping Selective memory protection is also provided through the Sigma 7 Map to insure the integrity of the operating system and individual user processes and data in a time shared environment User programs cannot accidentally or otherwise gain illegal access to virtual and physical memory areas not specifically allocated for their use The Map feature is of great value for reentrant programs which are of major utility in a time shared environment Common processes can be shared by several usar concurrently since their unique data areas appear identical in yiri memory but are actually dif ferent in physical memory By simply changing the user s map and program status double word registers program counter etc a common process can immediately start or con tinue operating for a different user Real Time Critical Real Time processes are given privileged sexuiees as in the Batch Process ing Monitor eee include Master mode operation Dedication of core memory space 1 0 devices I 0 channels CALL trap locations External Interrupts clocks fast register blocks etc A I O priority servicing l e Interrupt service Data and Command Chaining End Action I O service tn addition for the UTS environment the following services are posable nih Clock watchi
49. mpute mode 5 User Program Ready to execute and not in core conversational mode 6 User Program Ready to execute and not in core on line compute mode Executive Command Processor In the UTS environment Executive Commands are processed in an interactive man ran For Batch Jobs the normal Control Card Interpreter is needy The UTS Execu tive will use the same communication input buffer that the user s progran cup ioys When the user has explicitly or implicitly set the communication mode to Executive the Executive Command Processor will then process the input nesnage using its own echo table System Generation Every Executive Command will be treated as a priority interactive input which must be processed immediately it is not of higher priority than normale1 0 func tions For every Executive Command full conversational features must be used This means that a response to the user will be made immediately lt 3 seconds The response may be a WAIT to indicate that it will take some time for the Executive Request to be serviced such as loading a user program If an Executive Command format is in oe eee a diagnostic specifically indicating the error type will be returned Those ente Commands which do not produce any particular output will respond with a simple acknowledgement showing that the request has been received and that the user nat issue another Executive Command or other input The Executive Command processor uses
50. n as a canned package or cliche to the Executive Command processor for execu sequentially until the file end tion This facility permits complex operations to be wrapped up for repeated execu tions and it also allows program to generate a linked set of system processes for batch mode operations 33 Program to Program Intercommunication The UTS system will permit programs to call for the execution of other programs This mechanism will utilize the Load and Link facility whereby the program being called is treated as a Berane This means that a return to the calling program is antici ok sont deta fa pated upon completion of the called program s operation Communication between the two programs is accomplished by the registers and a communication file on secondary storage or in common dynamic storage top The calling program is assumed to be stopped while the called program is executing and may or may not be removed from physical core memory swapped There is no automatic copying of the calling program s context data for the called program the called programs will initialize its own operating needs based upon information transferred via the communication file or data area There is no sharing of virtual memory other than the common dynamic storage area foy batawi A acorta is to be used in a linked manner must be organized with a special front end convention as opposed to the normal program structure which
51. nd a conversa tional communication mode flag is maintained for each user channel Whenever a User 72 ac Tile USERS ANOR LIVE BUHBER IS MOEPEDENT OF i ee sy ge Cow YAT IE A REMTE USER 138 ACADEMY s ees ae ede mest wit DINS 1 OM AUTH ER AINE OTKEN ENH BER ERA IE re lS SDEMTS 7E0 BY JERMEN SSA K LIWE A YJE Are FIRES i G fear 1 EK i PN A DIAC EP CAPABILITY EXISTS 6 OVE OF ANDI CE war Cen 7 39 Terminaron Command is received i e LOGOUT the aral will be disconnected or power turned off EOT Provision will be made for installation assigment of special consoles for message addressing privilege functions and or priority ser vice Inter Console Service OF TEM It is efter useful and sametsimes essential to provide direct communications between user terminals in an interactive time sharing system This capability T provided by the UTS Antere terminal service and consists of two user functions and a program func tion The first user function is a simple store and forward messages switching opera e CovpPEQTED tion DIAL wheveby a user may address any ocher Termina H Specta liy the operator s console for delivery of a text message The second service provides linkage of two gt or more terminals to a single user program where the program normally operates for ie only a single user terminal This feature is extremely useful for oe demon strations group debugging etc The program function involves afc
52. ned on to receive a system on message after which the terminals will be turned off until a user begins normal opera tions No other Executive actions will take place other than normal set up for inter active and other requests that is communication processing and buffering for Executive requests will be provided User program communication buffers are not required until the user s process is loaded and active At shutdown time a system message to all active users will precede actually shut down operations No new users will be accepted into the system for the interval between the initial shut down announcement and system shut down After the interval System Generation an operator controlled parameter all currently active users still executing will have their processes automatically saved for resteut or terminated System Generation parameters or user option Communications Service Low Speed The UTS system includes a comprehensive and flexible communications package to service interactive operations It is dependent around character oriented full duplex hardware facilities which via the software provides message oriented input and output functions for user programs and ieee terminals ASR KSR Teletypes SDS Keyboard Display device 36 The UTS conmunications service consists of the following elements Terminal Status Management Low speed character oriented communications handlers input output Int
53. ner criteria wsteT A Scheduling Two forms of scheduling are operative in the UTS system Job Scheduling and Task aa Scheduling The former applies to a user job operating in the Batch Mode while the latter refers to elements of jobs of any kind for the multiprogramming environment i e interactive processing Job Scheduling Job scheduling is performed as under the Batch Processing Monitor i e a job stack is maintained on the disc which is organized on a rank ordered priority basis This priority is an administrative number assigned externally to incoming jobs In addition a For eroina ox interactive job can activate a background job by placing it in the stack via a monitor service sali AN sneer serie job can biace itself or be placed by the user on the production stack so that it is no longer interactive In this last instance the job is in save for restart form for subse quent execution Job Scheduling in the UTS aaa BPM system operates one job at a time from the production stack From a practical point of view it does not assume special situa cious where more than one background job is active or provide sophisticated scheduling rules e g automatic priority upgrading based on elapsed time and deadliness How eer users can if they so wish tailor job scheduling to their own needs by installing their own job scheduling modules at System Generation time Task Scheduling Task scheduling applies to the
54. ng service synchronous scheduling s tte Virtual memory space dedicated in all user maps Automatic swapping for non resident foreground tasks ey Non mapped operation for critical resident foreground tasks Real time processes fall into two general categories as far as responsiveness is concerned Critical Real Time Sg oe ces Tolerant Real Time In the first case responsiveness must be insured by constant core residency direct connection to interrupts dedication of system facilities etc In short system overhead must be reduced to a minimum tolerant real time processes are those which can afford some reasonable delay between the activating Signal and the time for process execution tr this case the real time process can be dynamically serviced by the UTS Monitor without unnecessary dedication of all operating facility needs particularly core memory However the implicit priority of any real time process is higher than a background job production or interactive users and are classed aa lt foreground operations Foreground processes can be either permanently installed for continual operation at System Generation time or dynamically loaded as a new job by the Operator In both cases once the real time task has been properly loaded into the system and activated it can utilize the privileged services provided by the UTS Monitor A Pseetaouad task can operate either in the Master Mode or in the Slave
55. on processor but through UTS service routines Such routines operate under the UTS Monitor and enable the system to continue normal operations as well as avoiding time consumption for a complete System Generation process The following system modifications are provided under both the System Generation processor and the UTS Monitor Subroutine Library maintenance New additions deletions replacements Public Service Programs Scheduling parameter changes ee Quantui values for user queues Number of interactive users in system Chirino Response time duty cycles Batch job time allocation Interactive status change conditions for various Monitor service requests Foreground identification and resource allocation Pevipheral device availability ae Auxiliary storage allocation changes Limits on user resource allocations User priorities Terminal directory changes e g system operator s station number Changes which are made only at System Generation time include Total system hardware configuration UTS system core organization and overlay structure Public Subroutine space assignments Scheduling queue structures Caber of queues decision rules Executive commands oe Accounting items UTS service extensions i 45 IV i UTS System Configuration Considerations The UTS system will require sufficient core residency for Monitor elements to execute in order to minimize
56. pendent context is separable from the process through isolable data and machine register storage areas The scheduling and switching of user environments is per formed by an external process i e an operating system Executive Processes which must control successive use by preserving user contexts themselves Recursive routines may be those which call upon themselves in a nested fashion last in ivsesout LIFO or may be first level machina dependent routines 1 6 interrupt routines which cannot expect context to be preserved by Ener processes ee MipensG ios Coming The UTS Monitor is designed to provide a spectrum of services ranging from Batch operations through real time tasks For each functional level there exists certain fundamental differences in scheduling logic as well as certain services which must be rendered Batch Level User jobs are organized in a stack fashion where the stack is a first in first out queue ordered by explicit priority Batch jobs are considered as Back ground operations with the lowest implicit priority in the system However opera tional efficiency for production jobs will not be jeopardized unnecessarily because of priority levels specifically in the area of system facility allocations At System Generation time or by operator action resources may be permanently or temp orarily allocated for batch operations so that implicit priority operations will not impede produ
57. r on line computing Needless to say the algorithm for scheduling can and should be adjusted to an installation s needs after such needs have become empirically determined For this reason maximum modularity and flexibility to make such changes are provided in the UTS design The rules for a user to move from one queue level to any other including the conversational queue are also variable for installations and can be changed by assembly and system generation loading They are not dynamically changeable during system opera tion Effectively queue management logic for the interactive level involves the decision rules for the following known events l Time quantum exceeded 2 Program return for various monitor services I O calls interactive input or output overlay linking etc 29 Another parameter specifiable at System Generation time and during system operation is the amount s time to be allocated for batch jobs This time is essentially a guaranteed portion of the interactive duty cycle which is always given over to background jobs It therefore will implicitly limit the maximum number of interactive users which can be served simultaneously The amount of time allocated to a Batch operation is cumulative that is if I O is requested CPU time is still available to it during the interactive duty cycle Thus a Batch job can operate intermittantly within the duty cycle to drive I O rapidly Howev
58. routines _ the map mode should not be used for foreground tasks Private copies of any required Coi subroutines will be provided by the loader If common reentrant subroutines are to be used then the map mode must be employed In this case it will be an appropriate real time service to dedicate virtual memory space in all maps so that map switching is eliminated except for FORTRAN subroutine local storage Foreground tasks can preempt core storage of all Background Batch and Interactive users except for I O buffers in use However other foreground tasks of lower priority will not be moved out of core memory unless they are mapped A foreground task operating in the Master mode can abort all I O service to other users and take over the machine but it is normally an indicat ton of system over load when foreground casks cannot eoupleke their executions Every foreground task connected to an interrupt will be responsible for preserving and restoring the current operational environment registers program status doubleword This will be done directly if the foreground task includes its own interrupt routine Bomer and by a a aunt handler when the foreground process is serviced by the system The latter approach is required for non resident foreground tasks A resident foreground task must be activated by an interrupt within 100 micro seconds after the occurrence of the interrupt This means that a foreground
59. rrupt configurations which could require CPU to CPU communications not provided for in the UTS Monitor 10 Resource Allocation The fundamental requirement for the UTS system is to perform effective resource allocation to concurrent system users on a dynamic basis The resources are varied in type number and mode of allocation some are more static allocations others very AOE Certain resources are very critical to system Loading capability and must be governable by a user installation Resources Available to a User Program Under UTS l Core memory space for execution 2 Compute time CPU 3 I O channel time and or assignment Gicvendiaa on type 4 I O peripheral devices 5 Active swapping storage on fast access disc 6 Permanent file storage on high capacity disc 7 Trap location gt Interrupt lines 9 Communication channels 10 Last memory blocks Ti Map space virtual memory space The above resources affect users in the following areas Convenient access for loading time Convenient access for execution time Restrictions on entry into the system executable or not FP O N m Restrictions on program execution size time facilities and priority Those resources whi h are sharable i e core storage auxiliary random access storage CPU time will be controlled by System Generation and Operator Key in para meters so that any one user or user program cannot freely degrad system performance or preempt s
60. ry point for error recovery and for manual inter vention must be made known to the UTS system prior to execution The routines at these ances points must be given the current user program status and register environ ment preserved for subsequent processing An error type code will also be passed to the error recovery routine op UTNE Given the case of a control program and a user s program such as the Debug service program and the user s object program provision must be made for proper return to a control point upon user intervention or an error condition If the user s program is being modified by the run time control program Debug then it must be loaded as part of the control program and treated as data They must share virtual memory Accounting The Accounting function under UTS will take into consideration the fact that multiple users are using system resources concurrently This means that for each user and job the time and space utilized by a user will be specifically accounted for A common process will be charged to user only when actually being used By definition all elements in the user s map which are actually in core memory will be chargeable except for the Monitor and where necessary a critical foreground process in all maps All secondary storage being held for a user will be charged including swap storage Wherever possible Monitor service for a user program will be clocked on the user s time Th
61. s a system parameter and may be changee by the customer installation It is only valid for a maximum number of users TA a given configuration depending upon whether a worst case or a probablistic loading environment is anticipated Performance will be based on SDS standard configurations and typical user software sizes Any variations in configurations or user software behavior e g sizes scheduling etc will affect sper FoTmanen figures and are the responsibility of mie customer 8 installation 48 Debug Service The UTS system provides an interactive Debug service program for use with Assembly language user programs When loading a program for debugging the user s map will share virtual memory between the object program and the Debug program Both will be loaded into core memory for execution The Debug program will provide the following services Dump memory locations in hexadecimal octal decimal instruction mncmontels and symbolically global symbols Locations will be referenced relatively to global symbols on ee New symbols may be defined for the object program Location contents can be altered Program insertions can be made Conditional selective snapshot dumps can be inserted and removed Conditional selective trace of program areas Start execution at any program location Dump or trace program environment data i e registers temp stack Modify program environment data Search
62. s for transfer to and from the high speed disc For example all data pages should be swapped if modifiable and protected elements are intermixed Logical Page Turning The UTS Monitor will offer a facility for a user program to operate within a _ smaller amount of physical core storage when the ytrtval addressing memory is large i This facility can be used where there is a maximum limit set upon a user s physical core space allocation or where there just is not enough physical memory available en stermoperating efftcienoyr instemt n overlay structure will be required from the user s program at load time which will describe a alta Suh oGmensh OWnenti O program segments for physical rather than virtual memory That is although the program will be written as if it had sufficient core space available to it a tree structure will show what logical pieces do indeed have to be resident at any given time The Batch system overlay mechanism can be used to provide this form of logical page turning since the organization requirements are similar The tree structure will show which pieces must always be resident which pieces must be in core concur PENTES and which pieces can be removed at certain times By making a reference to gTuR h an unavailable location the overlay tree will be consulted to determine what overlay action is to be followed The UTS Monitor will employ the map to make changes in th
63. ses on limp licie and explicit priority When physical pages are necessary low priority processes non vedutraae or data areas will be purged to secondary storage swapped Reentrant processes will not be saved since a fresh copy will be brought in when necessary For I O operations in progress for a user s program the I O buffer pages will be retained in core along with its context blocks continuing the DCB s etc If no operation is being per formed for a user program all of that program s core space will be purged teaying only dene information for future activation To control core space allocation a bit map of core memory pages is maintained by the UTS Monitor In addition the scheduling queues with their implicit and explicit priorities are used to find what must be brought in and what can be swapped out Each program s context area will contain a map image used to both establish the hardware map tien executing and to reset the bit map for memory when core space is released by swapping 21 Core memory management of the UTS system will Gecoonive special needs for user programs These include Core space dedication for foreground residency Specific core memory addressing space required for special hardware processors This would include restricting the use of this space for processes which could not easily be peeompeed i e sensitive areas This dacormavien will be _defined at S
64. st in overhead Time Sharing The sharing of computer system resources to provide processing service for several user functions related or independent where an individual job does not require all of the computer s time The allocation of such resources is based upon satisfying the response time needs of the participating tasks Thus critical on line processes can be interleaved with on line interactive Time Sharing Cont d Interactive Conversational Processing Remote Access _ Reentrant u Processes Recursive Processes operations and non priority production jobs can absorb any remaining computer time One of the major benefits of the time sharing approach to computer utilization Direct access to computational processes T convenient personalized services for a variety of new users and applications The needs of interactive computation include a satisfactory response time for non machine dialogue e g 1 5 seconds comprehensive easy to use service facilities and system reliability The physical extension of computer system access via communication lines Remote access may be provided for interactive production and critical real time operations 1 Those processes which permit independent users or user programs to execute them concurrently or in an interruptable sequence Reentrant processes are in pure procedure form where instruc tions are never modified and user de
65. the UTS Executive to recognize that it is a restart version in the user s account file and reopens all data files and DCB s that were active at the time of shutdown Program execution will resume exactly from the point of shut down or at the location suppiidd with the execution command from E user GO There will be a maximum limit established at System Generation iaei user ae for restart filed 9 j Smee sek goana re ce ae Carp ev pongas Ne fhe he T S5 Stem ee Processor and System Modification Since time sharing systems lend themselves to being highly variable in terms of _ configuration Ses nabe ue users types of user processes response needs etc it becomes critical to a user installation to be able to specify particular operating needs for its specific system configuration The mechanisms for this capability are eied primarily through System Generation parameters For those parametere which do not involve eeeuceurel changes in the system i e Spaca allocation additional changes in parameter values are made dynamically from the Operator Console The System Generation processor will operate in the minimal system configuration taking advantage of auxiliary storage Where more core memory is available time benefits PAX are derived from the additional PAA ES 44 All changes to a UTS system which can normally be expected to occur on a day to day basis will not only be changeable via the System Generati
66. time overhead for interactive and foreground operations This means that any UTS service required by an executing interactive conversational mode or foreground process must be core resident and should not be overlayed This applies also to any bookkeeping tables Administrative functions for initiating or terminating a process can be non resident Likewise service functions which may be required in the on line compute mode or Batch mode are candidates for overlay User programs which are swapped will also be handled to minimize response time That is user program areas e g context data which are necessary for on going Monitor s processing of users will be the last elements to be swapped or never swapped e g communication buffers parts of context area The minimal amount of core space required for an efficient UTS system Inter aekive plus Batch will be that space for resident monitor or processes and data monitor overlay area s user resident areas dynamically proportional to the number of active users currently on the system and sufficient available space for submerging interactive swapping overhead The latter factor is dependent upon the typical con versational process and or context size which must be donnei sue the typical Batch job size in core at one time and any foreground residency The size and number of such spaces will be determined by actual interactive process sizes and execution times This will be the con
67. tions Real Time Services They can also be used by an installation to extend the UTS Monitor services to user programs System Generation Selective Memory Protection The UTS Monitor allocates core memory according to operating needs and by memory protection needs That is the number of memory pages required is governed by the total memory size required as well as selective partitioning into different memory protection areas Monitor o No Access Public Routines l Read and Execute Only Context Area Read Only User Program ins eueetons Read and Execute Only User Data All Access Read Only co i l l i User programs must provide indications at load time of their process and data partitioning otherwise an All Access protection will be assigned No Access protection is assigned to any dedicated virtual memory space i e toa critical real time process while it is not peeves thereby minimizing environment switching no map changes Lock and key protection is used to guarantee the integrity of the Monitor and Executive areas from foreground tasks operating in the Master mode It will restrict _ such tasks from violating areas other than its own 19 Reentrancy The map feature of Sigma 7 has been designed to provide reentrancy capabilities for UTS storas By changing the user s map a common program process can be applied to a different user context and dataarea even though virtual addresses in the com
68. ts to do so when necessary Data associated with Executive functions can often be made non resident in core memory because of less frequent use or lower priority for esponse when core space is at a premium 13 Executive services of the UTS Monitor include the following Accounting Job Scheduler Batch Error processing and abort service I O resource allocation Storage allocation secondary storage File security User information services system status etc Checkpoint service save for restart Console Communications services Overlay loader Public subroutine control Main Monitor The hard core of the UTS Monitor consists of those Monitor functions which are constantly required to be in core memory for program execution I O Dispatcher I O Handlers standard peripherals Task Scheduler panes Interrupt processing Clock processing Trap processing Secondary storage access control Operator communication Communications handler for interactive users Symbionts and cooperatives when active Real time service routines Swap module Map Maintenance teore di iocatica File Management Basic Tables 14 Service Subsystems The UTS Monitor provides the operating environment for user programs which can be system service programs or private programs System services are public programs designed for multi use reentrant in the interactive case or any iastaliotion pro gram for the
69. uter process of indeterminate length Obviously a response time for completion of this process cannot be guaryanteed but the operating system must do the best it can on an equitable basis for all such users By defining system performance goals the conversational response time cycle can be made secure That is by establishing the maximum number of users the cut off point in CPU time allocation fora conversational process the conversational quantum etc it is possible to insure the proper turnaround time to a conversational input vor a general purpose time sharing system it is not possible to make assurances for turnaround time of any user computational process however for special applications here the process is a known quantity system design can account for some guarantee of fcuponse time at this level The UTS Monitor provides a Scheduling package for general interactive users with installation dependent parameters to govern the user service at the conversational and on line computing level Special application needs can be accommodated by modifica tion or extensions to this scheduling logic To accommodate effective interactive processing the UTS Monitor exploits the Sigma 7 Map feature for dynamic relocation of user programs and or data This facility permits users to share memory easily not only in terms of preserving virtual memory addressing but in allowing the use of non contiguous physical core me
70. versational FORTRAN plus the Text Editor facility The minimal core memory for a reasonable UTS system will be 48 65K however until the specific sizes and times for interactive processes are known capacity and performance figures cannot be established The Sua yp aeeae Stout ae Byker at on Aden Sonn nat inetd Contes F oak oaa wectdhng peat Nat g SO 00 Aesceata f Vha uncatovel 72 powered Fane 46 Auxiliary storage for a minimal UTS system will be based upon UTS system TOT and the number of active users acconmodated ConcuEnentry which is a function of core space and system efficiency This latter number dictates the amount of Swap storage fast RAD Scratch storage Permanent cee High capacity disc Library files A fon ad Magnetic tapes are required for system generating system entry of user eee programs data on to the discs disc purging and spill direct user access where necessary for user processes The minimum reduizement at PrEneEN AREAS to be at least two magnetic tapes 9 channel eh oper hardware requirements are oS 9 Rast Memory Blocks 2 Clocks Communications Interface Character oriented including interrupts i Madeipiekor IOP Re ee 2 Selector IOP Memory Protect Lock and Key MAP Decimal and Floating Point options Gard Reader E n Typewriter Printer ae At the present time the memory module ee aoe and number of ports canno P be specified fureut Coreg lin
71. ystem Generation time When necessary depending upon priority the required available space will be derived by swapping out the current residents If time erates special core needs will be accommodated by moving current occupants in core memory a system efficiency point of view nei mnie aera profitably organi so that protection types are Ogether For example all reentrant processes are physi ertain areas of core user context areas in others foreground s are physically top and the more dynamic swappable ele ments Of user programs are also co located Swappin As part of the a pasmie schedul iig of user programs in the eS dyste a swapping function is used Swapping involves the removal from physical core memory of a user s program and or RET make room for another aser It La etosely tied to the scheduling logic of the UTS system in that practical decisions must be made for the following Who executes next Who is transferred in next Who is removed from core next purge The logic of scheduled swapping is to always have a user process available for execution while other user processes are being swapped This requires sufficient core memory space to be available so that enough users can be resident to guarantee maximum over Lap of swapping I O time by user execution time Resident user execution times must be equal to or greater than the time to get other users ready swapped for execu tion ei

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