ACT (Amend Configuration Table)

1PASSWORDEnter Systems Password.
2DISC NOEither enter System Dic Number (range 001 to 377 octal),
3 The Configuration Table held at Sector 000042 on the stated disc is read into core. Amendments made to the table by the following instructions have no effect on the existing configuration until the system is re-bootstrapped off the relevant disc.
4AMEND DEVICE TYPES?Either ACCEPT to go to step 5,
or REJECT to go to step 8.
5TASK n IS xxxx?where n is the six-digit octal Task Number and xxxx is the four-character device identifier currently allocated to the task.
Either ACCEPT to leave the device type unchanged,
or enter new device identifier (see below),
or enter F if Task n does not exist (end of list – program goes to step 7).
Valid device identifiers are:
Alpha-Numeric Keyboard (8 or 16 character display).
16-line VDU (also valid for 8-line VDU).
24-line VDU.
DRI Printer.
CDC 400 lpm Printer.
BCL Serial Printer.
Centronics Printer.
VDU as emulator for a printer.
All required I/O Stations must be entered before Printers.
The first VDU input is assigned device codes 50/40, the next 51/41, etc. Where both 16- and 24-line VDUs are present, the order of input will be determined by their device codes.
6 Program returns to step 5 for the next task, until code F is encountered.
7 The amended table is written back to disc.
8AMEND TASK DATA?Either ACCEPT to go to step 9,
or REJECT to skip to step 13.
9TASK n BASE pp/ccss?Either ACCEPT to leave core partition unchanged,
or enter new Absolute Address of task’s Core Partition.
10If task is an I/O Station:
Either ACCEPT to leave command printer unchanged,
or enter Printer Code (one character A, B, ...)
or enter N if station is not allowed to command a printer.
  • At a one printer installation, the printer code should always be A.
If task is a Printer:
Either ACCEPT to leave start-up queue number unchanged,
or enter new start-up queue number (range 0 to max queue number).
  • This is the queue the printer will go to whenever the system is re-bootstrapped.
11 Program returns to step 9 for the next task, until the last task has been processed.
12 The amended table is written back to disc.
13AMEND PASSWORDS?Either ACCEPT to go to step 14,
or REJECT to go to step 17.
14PASSWORD n?Either ACCEPT to leave Password n unchanged,
or enter new password (max nine characters).
  • The new password does not appear on the screen.
15 Program goes to step 14 for the next password, until all four passwords have beedn processed.
16 The amended table is written back to disc.
17START FILE TABLE n?Either ACCEPT to leave start-up file table unchanged,
or enter new start-up file table number (range 0-3).

BOOT (Bootstrap Utility)

 STOW CONTROL?LOS Bulletin No 7 (February 1978):
Either ACCEPT to write the System Control Record to disc,
or REJECT to proceed without writing the System Control Record.

The usual practice is to ACCEPT, but this option is provided to avoid complications (e.g. if the required disc is not on-line).

1PASSWORDEnter Password 1.
2MASKEither enter LOS Switch Register Mask:
Recover from Security
Recover from Security after scratching Unit 70 Fixed Disc
Recover from Security Security after scratching Unit 70 and Unit 71 Fixed Disc
or enter MK1 “TCRD” Address:
Standard (8K) Package “HOST”
3SOURCE DISCEither enter LOS Source Disc Number,
or enter 5 if MK1 system is to be Bootstrapped,
  • The Source Disc must be loaded onto Unit 70.
4 The bootstrap procedure will be carried out when the Source Disc is on-line.

CALC (Octal Calculator)

1 Station displays column headings ---OCTAL--- DECIMAL
2 The calculator’s accumulator is cleared.
3+DECIMALEither enter Decimal Integer (+ or -),
or ESCAPE to go to step 1 to clear the accumulator (returns to PROGRAM? if the accumulator is already clear).
4 Program displays, on the same line, the double-word octal equivalent of the Integer input.
5 The integer input is added to the accumulator and the value of the accumulator is displayed, on the next line, in double-word octal and in Decimal.
6 Program goes to step 3.

CDL (Check Digit List)

Produces a printout of numbers with their associated check “digits”.

1 Station displays PRINT Q n where n is a Plain Paper Queue.
2FIRST NOEither enter Number at which the print-out is to start,
3LAST NOEnter Number at which printout is to end.
4 Program posts the printout to the indicated Print Queue and goes to step 2 for the next range.

COPY (Copy Discs)

This utility will copy any number of sectors from any part of one disc onto any part of another or the same disc (unless the receiving sectors are “protected”)

The target area is re-read and a software “hash-check” is carried out.

If the source and target areas overlap, it should be noted that the copying is carried out 8 sectors at a time, using a 1K-core buffer.

1PASSWORDEnter Systems Password.
Bulletin No 5 (February 1978): this utility is now inhibited rather than password protected.
2SECTORS (DECIMAL)Either enter the number of sectors to be copied,
or ACCEPT, if same number of sectors as last time (preset 12992 on entry),
or enter P if target area is protected (Protection Override) (program returns to step 2),
or enter OS to copy Operating System (program omits steps 4 and 6),
or enter CT to copy Configuration Table (program omits steps 4 and 6),
3SOURCE DISCEnter Source disc number in Octal.
4START SECTOR (OCTAL)Enter first sector of source disc to be copied.
5TARGET DISCEnter Target disc number in Octal.
6START SECTOR (OCTAL)Enter first sector of target disc to receive copy.
7PROCESS?Either ACCEPT to go to step 8,
or REJECT to return to step 2.
8 Station will BEEP on completion of the copy, and go to step 2.

DATE (Advance System Date)

1DD MMM YY ddd?Either ACCEPT to set the System Date equal to the displayed date (program goes to PROGRAM?),
or REJECT to return to step 1 (program displays the following day’s date),

DAY (Day of Week)

1DATEEither enter Date, in the format “d m y” of three numberic fields separated by a space (range 1 1 10 to 31 12 99),
2 Program displays Day of Week (e.g. TUE) for the given date in the twentieth century.
3 Program goes to step 1 for the next date.

DLU (Disc Labeling Utility)

1PASSWORDEnter Systems Password.
2DEVICE 000070?Either ACCEPT if indicated device holds the disc to be labelled,
or enter Device Identifier:
0 if Exchangeable Cartridge, 1 if Fixed Cartridge
Drive Code (usually 0)
Device Code (usually 70 or 71)
3DISC N0Either enter Disc No in Octal (range 001 to 377),
or ESCAPE to step 2.
4SECURITY?Either ACCEPT if this is a Security Disc,
or REJECT if this is a Master Disc.
5 Program will label the disc on the indicated device and go to step 3. A Security Disc will be marked “All sectors protected”, a Master Disc will be marked protected up to sector 000206 octal inclusive.


  1. There must be no disc Read/Write activity elsewhere in the system, the disc must be on-line and ready, and the Disc Number must be unique in the system before proceeding to step 5.
  2. The Disc Number should be marked on the cartridge in an indelible manner.
  3. The cartridge should NEVER be re-labelled unless the data it holds is no longer required.
  4. A Security Disc must not be re-labelled, and must not be renumbered, as a master disc. Disregard of this rule will place the installation’s data at dire risk.

Disc Labels

Each disc is identified to the operating system by Disc Number. For programming convenience the number is always given -in Octal, range 0 to 377.

The disc number is held in the first word of sector 40 (octal) of the disc, and this sector is therefore called the Disc Label. The second word of the label contains the number of the first “unprotected” sector on the disc (protection is a software feature designed to intercept any inadvertent write onto “read only” areas of the disc: LOS provides only one such area per disc).


000 to 007Reserved. Note that because MK I package discs hold the “TCRD” in Sector 408, a MK I package disc will acquire disc number 005 (with all sectors protected).
010 to 277The 1st and 2nd digits identify the “application” of this disc, the 3rd digit identifies the “type” of the disc as follows:
Master Disc.
“Daily” Security Copy 1 of the Master Disc.
“Daily” Security Copy 2 of the Master Disc.
“Special” Security Copy of the Master Disc
Working Version of Master Disc existing on a Fixed Drive.
300 to 377Reserved for systems purposes (temporary fixed disc labels, etc.).

LOS Bulletin No 30 (August 1978)

DSnn (Disc Security)

A new version of the disc security overlay, Module 006 is now available. A number of improvements have been made:

  1. The module is installation independent. The relevant-parameters (disc numbers etc.) appropriate to the installation are placed in System Module 11.
  2. Up to seven security cartridges may participate in the “daily” rotation for each Master cartridge.
  3. The “daily” rotation of each Master cartridge is independent of all other rotations. It is controlled by a 3-bit (1 octal digit) field in the System Control Record. One word (usually 0/0400) in the System Control Record may hold up to five such sequence control fields.
  4. The facility is provided to “skip” a security. This is useful after a recovery, because at the next security the system asks for the latest copy discs rather than the oldest.

To Skip a Security

Enter the security program as usual, but before typing the Password check that the security cartridges to be skipped are not online.

When the message TASK n AWAITS DISC x occurs, enter program R at another station and restart task n at the default address (ACCEPT).

To Abandon a Security


Disc Security Utility

A “daily” disc security program must be provided at an installation for the purpose of copying each Master cartridge onto Security cartridges (at least two securities, used in rotation, for each Master cartridge).

The standard disc security utility, described below, is specifically designed for one drive installations (where the exchangeable master cannot be secured without first securing, and finally recovering, the fixed master).

The utility is called from a user written program placed in System Module 11:

P1 = 002002
P2 = 0/0206 Module Number 006
P3 = Byte Address of Title
P4 = Byte Address of Password = 0/1300 usually
P5 = Address of Control Word, Phase 1 Control Block
P6 = Address of Control Word, Phase 2 Control Block


  1. The program runs at an I/0 station. On completion it returns to the PROGRAM? prompt. A suitable name should be placed in the “Input” Directory. Standard names:
    Daily Security, Unit 70
    Special Security, Unit 70
  2. The title (P3) appears on the I/0 station display, preceded by SECURITY.
  3. The password will normally be Password 1; i.e. P4 = 0/1300.
  4. Phase 1 is a direct copy: Master onto Security (both cartridges online together). Phase 2 is an indirect copy: Master via “fixed” onto security. The “fixed” cartridge is the Phase 1 Master (which is automatically recovered by a third phase).
  5. Phase 2 is required only where direct copying is not possible. If there is no Phase 2, P6 should be set zero. If there is a Phase 2, the operator has the option to carry out Phase 1 only.

Control Block

Each phase’s Control Block is n+2 words long, where n is the number of copy discs (to be used in rotation) associated with the relevant Master disc:


Control Word

B16:B13Cartridge Type Code:
B12:B10Number of copy discs. If this field is zero, one copy disc is assumed.
B9:B1Sequence field code. Not required (i.e. zero) if there is only one copy disc. Where more than one copy disc is to be used in rotation, this field defines the octal digit (3 bits) within the System Control Record which holds the current sequence number as follows:
Word offset of Sequence Field from beginning of System Control Record. Thus if the Sequence Field is at 0/0400, B9:B4 are zero.
Digit number within the word, numbered from the right, range 1 to 5. The digit itself, within the System Control Record, should be pre-set zero.

FLAG (Switch Program Inhibit Flags)

1PASSWORDEnter Password 1.
2 Program displays a list of program class numbers (one per line). Alongside each number is the class title (e.g. Class 1 = PROGRAMMERS' UTILITIES) and, if all users are currently prevented from entering programs of that class, the text *INHIBITED.
3SWITCH NOEither enter Class Number where Inhibit Flag is to be reversed,
4 The indicated Inhibit Flag is reversed, and the program goes to step 3 for the next class number, if any.

LIST (Module/Core Dump Print Program)

1 Program displays PRINT Q n where n is a Plain Paper Queue.
2MODULEEither enter Module number (Octal) and ACCEPT. go to step 5,
or ACCEPT only to go to step 3,
3CORE FROMEnter start core address (Octal).
4TOEnter end core address (Octal).
5TITLEEither enter up to 33 characters,
or ESCAPE to step 2.
6 Program posts the request to the print queue and goes to step 2 for the next request.

MOVE (Move Overlay Modules)

1PASSWORDEnter Systems Password.
LOS Bulletin No 5 (February 1978): this utility is now inhibited rather than password protected.
2TRANSFER?Either ACCEPT to go to step 3,
or REJECT to go to step 8,
3SOURCE FILE TABLEEither enter Source File Table Number (range 0:3),
4SOURCE MODULE Either enter Source Module Number (in Octal),
5TARGET MODULEEnter Target Module Number (in Octal).
  • The Target Library is that currently assigned to the issuing station by the F command.
where n is the number of sectors in the Source Module
Added by LOS Bulletin No 12 (April 1978):
Either ACCEPT if target is to be the same size,
or enter required number of sectors in Target Module (in decimal),
or ESCAPE to step 4.
  • If the target is smaller than the source, the high-order sectors of the source will be omitted.
  • There is no provision for amending the core loading point.
  • To amend the size of an existing module, set TARGET=SOURCE Module Number. It is always advisable to ensure there are sufficient spare sectors in the target library (the full number of sectors are required, even if the target already exists).
6 The Source Module will be copied to the Target Module, and the Target Library Index appropriately updated. The Target Module will replace any previous module with the same module number in the Target Library.
7 Program displays MOVED and goes to step 4 for the next transfer.
8COMPRESS?Either ACCEPT to go to step 9,
or REJECT to return to step 2.
  • Library Compression eliminates space within the Library which has become wasted due to the deletion of modules or due to the transfer of new versions from other libraries.
9 Program posts the Compression request to the deletions print queue and returns to PROGRAM?
LOS Bulletin No 12 (April 1978) changed the posting to the issuing station’s plain paper queue.
  • When the posting is processed by the printer program, the program will seize as workspace an area of the spool file equal in size to the Overlay Library. The message OVERLAY LIBRARY COMPRESSION IN PROGRESS is flashed to all stations (if there is insufficient free spool space an abort message will be flashed in lieu). The library is copied module by module to the work area. The work area is then copied back over the library. Unused sectors in the overlay library are zeroed, the Sectors in Use count in the File Status Block is updated and the System Control Record is stowed. Finally the message COMPRESSION ENDED is flashed to all stations. No printing occurs.
  • The Library compressed is that assigned to the issuing station by the F command.
  • Do not attempt to enter a program at any I/0 station whilst compression is in progress (a Program Hash Fail halt may occur).
  • If a system failure occurs during compression, it will be necessary to deem the library corrupted. It is therefore advisable to carry out a security copy operation beforehand.

OP (On-Line Program Amendment)

Program OP described below is available at all I/0 stations. It provides facilities to transfer Overlay Modules between disc and the station’s core partition, and to interrogate and amend any part of core.

Interrogation and amendment may be performed in Octal or Literal (ASCII) mode. When in Octal Mode the program attempts to decode machine instructions.

Do not amend the same Overlay Module simultaneously in two separate core partitions. Do not leave the station unattended whilst in program OP.

2 Numeric data entered below will be interpreted as OCTAL. The / character is treated as numeric and indicates bit input (0 or 1 must follow): e.g. 5/0000 is interpreted as 012000. The . character is treated as numeric and adds bit-16 to the input; e.g. 5/0000. is interpreted as 112000 (allows Byte Addresses to be input).
3 Any non-numeric character terminates an octal field. The ACCEPT key must not be used as a terminator. The REJECT key is used to cancel an error, and the ESCAPE key will always lead back to PROGRAM? selection.
4 The station cannot obtain Command Mode within this program.
5OP?Either enter nR to read Overlay Module n from disc (go to step 6),
or enter nW to write Overlay Module n back to disc (return to step 5) (ERROR if Module was not first read from disc),
or enter xA to set MEMORY ADDRESS to address x (go to step 7),
or enter xI to set MEMORY ADDRESS to the address contained in core location x (go to step 7),
or enter x[space] to display ASCII at address x (return to 5) (display ends on encountering a NUL byte),
6 The Overlay Module is read into the station’s core partition at its proper offset. MEMORY ADDRESS is set to the absolute address of the first word of the Module within the partition.
7a x d
is a six digit octal number, the value of MEMORY ADDRESS.
is a six digit octal number, the CURRENT contents, in core, at the MEMORY ADDRESS.
is a 12 character string, the machine instruction DECODE of x.
Either RESET to re-examine x and d at a (return to step 7),
or enter n[RIGHT ARROW] to increment a by n words (n = 1 by default) (return to step 7) (each word is displayed in the format a x d)
or enter n[LEFT ARROW] to decrement a by n words (n = 1 by default) (return to step 7) (each word is displayed in the format a x d)
or enter yO to set MEMORY ADDRESS to the value (y + partition base), i.e. to the offset y within the station partition (return to step 7)
or enter yA to set MEMORY ADDRESS to the Absolute value y (return to step 7)
or enter yI to set MEMORY ADDRESS to the value contained in Absolute Core Location y (return to step 7),
or enter y[SPACE BAR] to display ASCII at absolute address y (return to step 7) (display ends on encountering a NUL byte) (y = a by default),
or enter l and ACCEPT to load l into a (go to step 8)
16 line VDU: Do not accept; use [DOWN ARROW] or [GS],
or enter l and REJECT to load l with bit-17 set into a (go to step 8) (allows Offset addresses to be input)
16 line VDU: use [FS],
or enter y­ to switch to Literal (ASCII) input (go to step 10) (y=a by default)
or ESCAPE to OP?
8 Program displays x d the new values of CURRENT and DECODE at the MEMORY ADDRESS.
9 MEMORY ADDRESS is incremented by one and the program returns to step 7.
10LIT:Enter ASCII characters and ESCAPE to step 7.
  • All characters entered are loaded (2 characters per word) except the ESCAPE character.
  • Lower case input is converted to upper case.
  • MEMORY ADDRESS is incremented by one after every second character.
  • If an odd number of characters is entered the second byte of the last word is left unaltered.
  • Back-spacing does not correct a typing error, but simply loads ASCII BS into the current byte.

PLM (Program Library Maintenance)

2AMEND DIRECTORY?Either ACCEPT to go to step 3,
or REJECT to go to step 10,
  • There are two seperate directories, one for Input programs and one for Print programs.
3"INPUT"?Either ACCEPT to amend the I/0 Station directory,
or REJECT to amend the Print directory.
4NAMEEnter up to 4 characters.
  • A short name will be automatically space-filled to four characters.
5 If the name is not already in the directory Station will BELL and display NEW NAME.
where n is module number in octal
Either ACCEPT to leave n unchanged,
or enter x where x is the required module number in Octal,
or enter 0 to delete the name from the directory and go to step 9.
where x is a core location (absolute or offset)
Either ACCEPT to leave the logical entry point x unchanged,
or enter y where y is the required entry point (absolute or offset).
8 The directory entry will be added or amended as appropriate, and the program goes to step 2 for the next operation.
9 Station will BELL and display x DELETED where x is the program name, Program goes to step 2 for the next operation.
10NEW OVERLAYEither ACCEPT to go to step 11 to add a new overlay module to the library,
or REJECT to go to step 2.
11MODULEEnter module number in Octal
12 If the module number is already in use, station will bell and display LOADED and will return to step 11.
13SECTORS (DECIMAL)Enter number of sectors required (in decimal) (Range 1-13)
14START LOC'NEnter Core address (absolute or offset).
15AUTO-RESOLVE?Either ACCEPT if the overlay begins with a block of offset addresses,
or REJECT otherwise.
LOS Bulletin No. 3 (January 1978): This prompt has been removed. Henceforth, offset address resolution will be carried out when, and only when, overlay modules are fetched into core by program name.
16 Disc space is reserved for the new overlay module and its particulars are added to the index. Program goes to step 2 for the next operation.

PMAP (Print Program Map)

Produces a print-out, in Overlay Module Number order, giving details of all overlay modules.

1 Program displays PRINT Q n where n is a Plain Paper Queue.
2PROCESS?Either ACCEPT to print the entire map (go to step 4),
or enter first module number in octal,
or REJECT to return to PROGRAM?
3LASTEither ACCEPT if only one module is to be printed,
or enter last module number in octal.
4 Program posts to print queue and returns to PROGRAM?

R (Restart Task)

This program may be used after a TASK HALTED message has been issued by the system; it enables programmers to restart programs under test at any point.

1 Program may display INHIBITED! and go to PROGRAM?
Enter program FLAG and switch the programming utilities flag.
2TASK NOEnter Task Number (in Octal) of the task to be restarted.
3ADDRESSEither enter Core Address (absolute or offset) at which the task is to be restarted,
or ACCEPT to restart at the beginning of the task control program.
4 If the task is indeed halted, it will now restart at the indicated address and program returns to PROGRAM?

READ (Disc Read Utility)

1PASSWORDEnter Systems Password.
2DISC NO.Either enter Disc Number holding sector to be read,
or ACCEPT to go to step 8 (Read Record).
3SECTOREither enter Absolute Sector Number in Octal,
or enter n and REJECT to go to step 6 (Overwrite),
4 Program displays the core buffer address into which the sector has been read, followed by the 128 words of the buffer in 6-digit octal (8 words per line).
5 Program goes to step 3.
6OVERWRITE?ACCEPT to write the core buffer to sector n.
  • If n = 0, the buffer will be written back to the same sector as was most recently read or written.
7 Program goes to step 4.
8FILE IDEither enter 2-digit Octal File Identifier,
9TEST?Either ACCEPT if the "TEST" option is to be applied on fetching the record at step 10,
or REJECT otherwise.
10KEYEither enter Record Key in the format applicable to the file,
or ESCAPE to step 8.
11 Program displays the Core Address of the record within its transfer buffer, followed by each word of the record in 6-digit octal (8 words per line).
12 Program goes to step 8.

RP (Reprint Utility) (released September 1978)

1If there is more than one printer:
Either enter Printer Identification letter,
2 Progam displays PRINT Q n where n is the Reprint Queue of the selected printer.
  • Each printer has its own reprint queue; re-printable work processed by the printer is placed into its reprint queue regardless of its queue of origin.
3SERIAL NOEither enter Serial Number of the document to be reprinted,
or ACCEPT if this is an enquiry only,
  • If more than one document is to be reprinted, enter the oldest serial number.
4 The program searches the reprint queue for a document with the specified serial number. As the search proceeds, the program displays the four character program name and the serial number of each item in the queue.
5If the serial number is found:
Either ACCEPT to request a reprint and go to step 6,
or REJECT to go to step 6,
6  The program displays the next item in the queue and goes to step 5. When the end of the queue is reached, program goes to PROGRAM?.


Items become available for reprinting. (i.e. are posted to the reprint queue) immediately printing of the original begins. Thus, if the printer breaks down during the printing of the original it is possible to obtain the reprint (if another printer is available to print it) before the original. However, the file updates that would have been done whilst printing the original will not yet have been completed; indeed they will only be carried out if the original printer can be repaired without having to re-bootstrap the operating system.

S (Send Message)

1TASKEither enter Task Number (in Octal) of destination,
or ACCEPT if to be sent to all Stations,
2TEXTEnter message text.
3 The text will be flashed (with BEL tone) to the destination station(s) and program goes to step 1.

SE (System Enquiry)

Standard Phases

GET 04/1430
PROGRAM? prompt
GET 13/0350
COMMAND? prompt
GET 03/0706
PAUSE 04/1523
Print Program idle
PAUSE 04/0207
Print Program awaiting free Buffer
PAUSE 04/0345
Print Program suspended by operator
PAUSE 03/1133
Task Halted by Program
PAUSE 13/0355
I/O Station queued for Command Handler

ZERO (Zeroise Sectors)

1PASSWORDEnter Systems Password.
LOS Bulletin No 5 (February 1978): this utility is now inhibited rather than password protected.
2DISC NOEnter Disc Number (octal).
3START SECTOR (OCTAL)Enter Start Sector Number (octal).
4SECTORS (DECIMAL)Enter Number of Sectors to be cleared, in decimal.
5PROCESS?Either ACCEPT to continue,
or REJECT to go to step 2.
6 Station will bell and return to PROGRAM? on completion.