100 BEGIN
110     COMMENT TPK ALGORITHM IN ALGOL 60;
120 
130     REAL PROCEDURE FN(X);
140     VALUE X;
150     REAL X;
160     BEGIN
170         FN := SQRT(ABS(X)) + 5 TIMES X * 3
180     END;
190 
200     COMMENT MAIN PROGRAM;
210     INTEGER N, J;
220     REAL ARRAY A[1:11];
230     FILE OUT DCO 19 (1, 10);
240     FILE IN DCI 19 (1, 10);
250     FORMAT NUM(R11.4);
260     FORMAT PROMPT("PLEASE ENTER 11 NUMBERS");
270     FORMAT RESULTS("RESULTS ARE");
280     WRITE(DCO, PROMPT);
290     N := 11;
300     FOR J := 1 STEP 1 UNTIL N DO
310         READ(DCI, NUM, A[J]);
320     WRITE(DCO, RESULTS);
330     FOR J := N STEP -1 UNTIL 1 DO
340     BEGIN
350         REAL RESULT;
360         FORMAT TOOLARGE("TOO LARGE");
370         RESULT := FN(A[J]);
380         IF RESULT GTR 400.0 THEN
390             WRITE(DCO, TOOLARGE)
400         ELSE
410             WRITE(DCO, NUM, RESULT);
420     END;
430 END.

The line numbers are for entry on CANDE and are not used by the program itself. Keywords like INTEGER are reserved and do not need to be quoted.

On line 170, FN := SQRT(ABS(X)) + 5 TIMES X * 3, note that the multiplication operator is the Algol glyph × but we can't type that so we use the text equivalent TIMES. * here is the exponentiation operator. Similarly on line 380 we use GTR to stand in for >.

I/O is not a part of Algol so each implementation does its own thing. Burroughs did it as follows:

• FILE introduces an I/O channel. The 19 refers to the device, here the data terminal. Other devices are listed on p105 of the manual. The (1,10) refers to the buffer size used. Note that input and output each needs a separate FILE variable. FILE declarations are block-scoped, so here the devices are closed automatically at the program END.
• FORMAT works like in Fortran to define how input should be parsed and output presented. We use it here for real numbers (NUM) and some string constants (eg PROMPT).
• READ and WRITE do the actual I/O, taking the file, format and data as their parameters.

On line 390, I originally had WRITE(DCO, TOOLARGE); ie with a semi-colon on the end. This was correctly raised as a syntax error by the compiler as this is not an end of statement situation as the IF clause extends to the ELSE on the next line. The Dartmouth Algol compiler allowed this.

Apart from this, the rest of the implementation works the same way as standard Algol.

When executing this you need to enter numbers in floating point, eg 1.0 instead of 1.

The code and execution transcript for this can be found on Github.

The manual is rather terse, as it is intended as a reference rather than a tutorial, and also does not list in a single place what extensions have been added. However, the text follows the format of the Revised Report on the Algorithmic Language Algol and when each part of the language is introduced in Backus-Naur form it prefaces each of them with a tag:

• 1 means this is the same as the standard
• 2 means this has differences
• 3 means this is new syntax

So this is not a comprehensive list, but some of the interesting extensions I noted while reading the manual:

• Conditional expressions: K := (IF J = 0 THEN 0 ELSE 1 / J);.
• Fill an array: REAL ARRAY A[1:11]; FILL A WITH 42;
• ZIP to run an external program in the background: ZIP("HELLO ", "RUPERT "); would run the hello world example we did earlier.
• TIME(0) gets the current date.
• WHEN(5) pause for 5s
• Can recover from errors eg divide-by-zero via testing flags
• A CASE statement

See the reference manual from 1969 on bitsavers. The other Algol material noted on the Dartmouth DTSS article may also be useful.

I welcome any questions or comments, and also especially any corrections if I have got something wrong. Please email me at rupert@timereshared.com and I will add it here and update the main text.

By default, files are not visible to other time-sharing users on CANDE. With the UNLOCK command you can make them visible and read-only to others; PUBLIC makes them read/write. LOCK returns files to their default state. You can see the protection on files with LIST FILES.

UNLOCK HELLO
#
LIST FILES
09/26/26 RUPERT         02:27 PM
NAME    TYPE     RECS SEGS   CREATED   ACCESSED  W/R  W/B  S-F LOCKD BY
HELLO   BASIC       4   10  09/23/25 * 09/26/25   10  300    7  UNLOCKD
HELLO   OBJ(B)     13   13  09/23/25 * 09/26/25   30   30    7  UNLOCKD
       2  FILES         23  SEGMENTS      17  RECORDS

Other users can access them by adding a / then the user name, eg RUN HELLO/RUPERT.

It's also possible to apply more granular permissions with a GUARD file. You run the interactive GUARD command to create a list of names and permissions, then apply via LOCK WITH. For example, to grant read only access to a staff group containing FRED and MARY:

GUARD
 RUNNING
        

NEW OR OLD LOCK FILE??NEW
LOCK FILE NAME??STAFF
READ ONLY NAMES??FRED,MARY
READ/WRITE NAMES??
ADD, DELETE, LIST, SAVE, OR QUIT?
?LIST
(R) FRED
(R) MARY
ADD, DELETE, LIST, SAVE, OR QUIT?
?SAVE
LOCK FILE SAVED.
ADD, DELETE, LIST, SAVE, OR QUIT?
?QUIT
THANK YOU.


 END GUARD .0 SEC.

LOCK HELLO WITH STAFF
#

Note that this security model only applies to CANDE. Batch jobs can access any file on the system.

You can run a sequence of commands - like a Unix shell script - using the SCHEDULE facility. First you need to create a DATA file containing the commands. DATA files do not have line numbers and their contents can be entered by starting a line with ?DATA and terminating with ?END.

CREATE HRUN DATA
FILE:HRUN - TYPE:DATA  -- CREATED
?DATA
 OK
LOAD HELLO
LIST
RUN
?END

You then issue the SCHEDULE command, giving the file to send output to as the second parameter. The AFTER time parameter is optional, without it the job should be scheduled as soon as possible.

SCHEDULE HRUN TO HOUT AFTER 1530

You can then use STATUS with the output file name to see its status, or STOP to cancel it.

STATUS HOUT
SCHEDULED

However, in practice I have found that these jobs never get executed - they stay in state SCHEDULED forever. Let me know if you find a way to get this working.

This is a way to make a program send input/output to a different place without changing the source code. Say you have this simple Algol program:

FILE:P42    -10/02/25  6:41 PM.

100  BEGIN
110  FILE OUT TYPEWRITER 19 (1, 10);
120  INTEGER J;
130  J := 42;
140  WRITE(TYPEWRITER, /, J);
150  END.

which if run prints 42 to the user's terminal

RUN
 RUNNING
        
42,

 END P42 .0 SEC.

In the code, the FILE statement defines an output file called TYPEWRITER to attach to unit 19, which is the user's terminal. (We'll go into I/O on Algol in more detail in a later post).

Using the CANDE EQUATE verb you can redirect this to a file or another device. The file must already exist before running. So if you wanted to send output to MYOUT:

CREATE MYOUT
SAVE
LOAD P42
EQUATE TYPEWRITER=MYOUT
RUN
 RUNNING

 END P42 .0 SEC.

LIST MYOUT 

FILE:MYOUT  -10/02/25  6:37 PM.

 42,

 END QUIKLST .0 SEC.

Note that the EQUATE only lasts until the next RUN command, but you can stack up more than one EQUATE before running.

There's a way to send single line messages to other users or the operator via the TO command. For example, if It was logged in as GUEST and wanted to send a message to RUPERT:

TO RUPERT HELLO

and if he was logged in he would see:

 ** FROM GUEST   (03)     HELLO

With the first parameter set to SPO it gets sent to the operator's console.

TO SPO HELP I LOST MY TAPE

and they would see:

R ** FROM GUEST(03) HELP I LOST MY TAPE

It's not possible for an end user to add new verbs to CANDE, nor can they use other compilers beyond those already defined. However, all Burroughs sites would receive the source code for CANDE so it would be possible for the system programmers to add these. For example, Georgia Tech added a CALL command to execute programs like GPSS or APL.

Finally here's a list of all commands on CANDE.

In the table, f is a file name; if not given, it assumes the work file. Note that if you have say a file FOO which you load into work and then change, COMPILE will compile that working file, but COMPILE FOO will compile the old version on disk.

Several commands have synonyms not listed here: for example DO does the same as EXECUTE

On bitsavers, the Time-sharing System User's Guide is the best first reference; note this is from a different version of MCP so some of the commands may differ. The Georgia Tech B5700 Time-sharing System Manual is a more complete reference, giving examples of each command, but note this also contains extensions added by Georgia Tech not available on the base Burroughs system.

Also of interest is The Complete CANDE Primer in the Charles Babbage Institute Burroughs collection. However this is from 1980 so for a much enhanced version of CANDE compared to what we have today.

I welcome any questions or comments, and also especially any corrections if I have got something wrong. Please email me at rupert@timereshared.com and I will add it here and update the main text.

On retro-b5500. halt/load the system, and enable time-sharing by entering CE on the operator console. navigate to the terminal (DCA) window and click connect.

On simh, start the system - time-sharing is already enabled if you used the quick-start - then use telnet to connect to port 5500 on localhost. Then give your user name and password.

B5500 TIME SHARING - 01/00, STATION 02
ENTER USER CODE, PLEASE-RUPERT
AND YOUR PASSWORD
RUPERT@@
09/23/25 12:11 PM.
GOOD AFTERNOON, RUPERT LANE     YOU HAVE STATION 02

#

Once logged in, you can either edit a work file or issue commands, in an interface similar to Dartmouth DTSS.

Input lines should be less than 72 characters long. You can use backspace to correct mistakes and Enter to terminate a line - this is a convenience of the emulator; on the real system you'd use ' to backspace and ← to finish a line.

A line starting with " is treated as a comment, ie just printed on the teletype but not saved or processed.

More than one command can be given on a single line by separating them with ;. Commands can usually be abbreviated, eg LIST can by typed as L.

If you get an error message, typing ? will often provide more details.

If you get stuck, eg a program is in an infinite loop, you can interrupt it back to the command level by pressing break, which is Control-E on simh or Control-B on retro-b6600.

CANDE has the concept of a work file which is a temporary copy of a program on disk. You can make a work file by creating a new file or loading from an existing disk file.

File names in CANDE are 6 characters long and must start with a letter.

To create a new work file, use CREATE name type where name is the file name and type is a programming language: BASIC, ALGOL, FORTRAN, or COBOL. You can also set type to be SEQ (for general line numbered files) or DATA (for un-numbered line files).

CREATE HELLO BASIC
FILE:HELLO - TYPE:BASIC  -- CREATED

To load an existing file, use LOAD

LOAD HELLO
FILE:HELLO - TYPE:BASIC  -- LOADING
4 RECORDS LOADED.

Typing a line starting with a number adds to a program or replaces the line if it already exists. Typing a line number on its own will delete that line. Lines can be entered in any order.

You can use the SEQ command (or just the abbreviation +) to automatically create a line number for each line you enter. Terminate it by pressing Enter on a blank new line.

SEQ
100FOR I = 1 TO 5
200PRINT "HELLO, WORLD"
300NEXT I
400END
500
#

As well as retyping a line, there is also the FIX command which can delete or change part of a line.

FIX's syntax is

    FIX line-number delimiter old delimiter [new]

So for the line

    200 PRINT "HELLO, WORLD"

you can change this to "HELLO, EARTH" with

    FIX 200 /WORLD/EARTH

and delete HELLO with

    FIX 200 /HELLO, /

The delimiter used above was /, but this could be any character. Note that only two delimiters are used, compared to say Unix sed where you'd do s/world/earth/.

Note also that FIX only makes changes the next time the file is used (eg on LIST or RUN) - so any errors in your FIX syntax will be presented then, not immediately.

FIX can also be abbreviated to just *.

COMPILE will compile your work file, printing out any errors if found. EXECUTE will run the compiled file. Typing RUN will compile and execute, skipping the compile if the program has not changed.

RUN
 WAIT.

 COMPILING.


 END COMPILE .0 SEC.

 RUNNING
        

HELLO, EARTH
HELLO, EARTH
HELLO, EARTH
HELLO, EARTH
HELLO, EARTH


 END HELLO .0 SEC.

You can use LIST to list out your program; rather than listing the whole file you can give a single line number or a range as parameters, eg LIST 200-300. PRINT is like LIST but will omit the banner.

PRINT 200-300
200 PRINT "HELLO, EARTH"
300 NEXT I

You can see what files you have in your disk area with FILE or for slightly more detail, LIST FILES.

FILES
 *HELLO  HELLO
#
LIST FILES
09/23/25 RUPERT         12:57 PM
NAME    TYPE     RECS SEGS   CREATED   ACCESSED  W/R  W/B  S-F LOCKD BY
HELLO   BASIC       4   10  09/23/25 * 09/23/25   10  300    7
HELLO   OBJ(B)     13   13  09/23/25 * 09/23/25   30   30    7
       2  FILES         23  SEGMENTS      17  RECORDS


 END LFILES .0 SEC.

You can manipulate files with COPY, RENAME and REMOVE, as well as APPEND and MERGE to combine several files.

Type BYE to end your session. If you have modified your work file, you will get an error; you can either type SAVE to save it or DELETE to discard.

When you log off you will see some statistics

 ON FOR  3 MIN, 45.2 SEC.
 C&E USE .0 SEC.
 EXECUTE .0 SEC.
 IO TIME .0 SEC.
 OFF AT   6:50 PM.
 GOODBYE GUEST
07/14/25

If you enter ? to find out details of an error before you have submitted any commands at all, you get:

?
I AM THE GENIE OF THE DISK--WHAT IS YOUR COMMAND?

If you halt/load the system while still connected to the terminal you will see the following when the system comes back up:

P 
 L 
  o 
   P 
RESTARTING . . PLEASE WAIT

In the next post I will go into more details on some advanced CANDE commands.

On bitsavers, the Time-sharing System User's Guide is the best first reference; note this is from a different version of MCP so some of the commands may vary. The Georgia Tech B5700 Time-sharing System Manual is a more complete reference, giving examples of each command, but note this also contains extensions added by Georgia Tech not available on the base Burroughs system.

Also of interest is The Complete CANDE Primer in the Charles Babbage Institute Burroughs collection. However this is from 1980 so for a much enhanced version of CANDE compared to what we have today.

I welcome any questions or comments, and also especially any corrections if I have got something wrong. Please email me at rupert@timereshared.com and I will add it here and update the main text.

The B5500 was a 48 bit machines with 6 bit characters and could have up to 32 kwords of core memory. It could contain one or two CPUs, with the second CPU only doing compute rather than I/O. The B5000 only supported drum storage but the B5500 brought a fast head-per-track disk. Each stored 48 or 96 Mbytes and in theory up to 20 could be attached.

A dedicated teletype console, called the SPO (supervisory printer/keyboard), allowed an operator to interact with the system.

A data controller allowed up to 15 terminals - initially teletypes - to be attached for use by time-sharing or other programs.

There was also the usual peripherals - magnetic tape drives. card punch, card reader and line printer.

B5000 System Diagram. Note this is for the B5000 so shows a drum instead of the disk used on the B5500. Source: The Descriptor at bitsavers.

As noted in the introductory, the original drum-based version of MCP was modified to use disks and called the Disk File MCP (DFMCP); another version used the data concentrator for terminal access and was called the DCMCP; finally there was the time-sharing variant of MCP was called the TSMCP.

The TSMCP allowed both batch and time-sharing jobs to be run simultaneously. The main way that time-sharing users communicate with the system is a job called CANDE, standing for Command and Edit. This managed communication with each data line, allowing users to log in, edit programs and run jobs.

Memory was divided into two sections ('the fence'); the MCP and CANDE run on one side, user programs run on the other. The TSMCP would schedule time-sharing jobs so they would receive regular short time-slices, while batch jobs would queue up until they had enough memory to run for longer time-slices.

The system had no assembler - it was programmed entirely in high level languages. Initially Algol and COBOL was supported, with BASIC and Fortran being added later. Compilers would generate machine code directly.

This lack of an assembler even extended to system software, with the entire operating system being written in an extended form or Algol called ESPOL that could do low level operations not defined in pure Algol. For example, you could access any position in memory via an array.

This also meant that the machine was never used 'bare' - programs would not run directly on the hardware, they would always be run under the MCP.

Machine operations were done with a push down stack, so to add two numbers you would push the numbers onto the stack and then execute an add, leaving the result on the top of the stack. This made writing a compiler much easier as expressions could be translated into stack operations without having to deal with temporary memory locations. This also enabled easy relocation of programs and support for recursion.

Larger areas of memory, such as programs or arrays, were arranged into segments that could be swapped in and out of memory, allowing programs or data sets larger than core to be handled. Each compiler organised how it broke down programs into segments, which did mean there was no facility to link together code from multiple languages.

Segments were tagged as either data or code, so it was impossible for user programs to modify its own code.

You may have noticed while installing the system there was no need for a system generation phase where you tell the OS what hardware it can access. Instead, the MCP senses what hardware is connected, and can cope with peripherals, memory and even the second CPU being temporarily offline without restarting.

Files had a two part name separated by a /, such as HELLO/GUEST. The second part indicated the grouping of a set of files, in this case the time-sharing user GUEST. This is not a directory, however: you could call a file HELLO/XYZ without having to create XYZ first.

Magnetic tape files are device independent: if a job wants to read from a certain tape file, it just needs to call for the tape file name. MCP senses what tapes are mounted where and will direct the read to the correct device.

See the documents on bitsavers, especially the Time-sharing System User's Guide and The Descriptor.

I welcome any questions or comments, and also especially any corrections if I have got something wrong. Please email me at rupert@timereshared.com and I will add it here and update the main text.

Type ./build.sh. This will download simh and the mcp-kit under packages/, build the simh b5500 binary and copy files. The file structure on your PC will now look like

It will then proceed to

• cold boot the B5500 from a punched card image
• set up the virtual disks and install MCP files
• add extra software that has been collected.
• set up time-sharing and create users

Installing MCP on simh. Source: Rupert Lane. License: CC0.

This will take around 5 minutes and will only need to be done once. If you ever need to rebuild the system, run build.sh again; it will not re-download the package files.

Type ./run.sh. After a few seconds the system will say it is ready for connection. Using a telnet client, connect to port 5500 (eg via telnet 0 5500.)

In the telnet session, type your username and password. Your screen will look something like this, with the window on top being the console and the one below the user session.

Login to CANDE on MCP under simh. Source: Rupert Lane. License: CC0.

Here's an example of a complete session.

$ telnet 0 5500
Trying 0.0.0.0...
Connected to 0.
Escape character is '^]'.


Connected to the B5500 simulator DTC device, line 0


B5500 TIME SHARING - 01/00, STATION 02
ENTER USER CODE, PLEASE-GUEST
AND YOUR PASSWORD
GUEST@@@
09/02/25  6:04 PM.
GOOD EVENING, GUEST USER      YOU HAVE STATION 02

#
CREATE HELLO BASIC
FILE:HELLO - TYPE:BASIC  -- CREATED
100 FOR I = 1 TO 5
200 PRINT "HELLO, WORLD"
300 NEXT I
400 END
RUN
 WAIT.

 COMPILING.


 END COMPILE .0 SEC.

 RUNNING
        

HELLO, WORLD
HELLO, WORLD
HELLO, WORLD
HELLO, WORLD
HELLO, WORLD


 END HELLO .0 SEC.

LIST


FILE:HELLO - TYPE:BASIC  --09/02/25  6:08 PM.

100  FOR I = 1 TO 5
200  PRINT "HELLO, WORLD"
300  NEXT I
400  END


 END QUIKLST .0 SEC.

SAVE
FILE:HELLO - TYPE:BASIC  -- SAVED.

BYE
 ON FOR  4 MIN, 00.4 SEC.
 C&E USE .0 SEC.
 EXECUTE .0 SEC.
 IO TIME 2.9 SEC.
 OFF AT   6:08 PM.
 GOODBYE GUEST
09/02/25

After we login, we create a new BASIC file called HELLO, and type in the program using line numbers. RUN will compile and execute it, LIST will display a listing.

Type BYE to log out. If it complains about unsaved work, you can either type SAVE to keep it on disk or DELETE to discard your work.

There is no shutdown process for the operating system itself. Go to the emulator window and type Control-E to interrupt it, then q to quit.

You can restart MCP with ./run.sh as needed.

I welcome any questions or comments, and also especially any corrections if I have got something wrong. Please email me at rupert@timereshared.com and I will add it here and update the main text.