TOPS-10: BASIC

As in 4th edition Dartmouth BASIC, the DEC version supports

• LET (optional) to define variables, DIMENSION to declare arrays.
• PRINT, INPUT for I/O
• READ, DATA to encapsulate data in a program
• IF … THEN for conditionals
• FOR .. NEXT for loops
• GOTO, ON … GOTO, GOSUB & RETURN for transfer of control.
• DEF FN for single line functions

END is needed as the last statement of the program.

The default variable type is floating point. String variables are available by suffixing the name with a $. Both types can be formed into arrays using DIMENSION. There is no integer type, but there is a matrix capability via the MAT keyword.

It also has these common extensions to Dartmouth 4th edition

• STOP will half the program
• REM for comments
• CHAIN to load in a new program from the existing program
• Page and margin control
• String concatenation via +, string/number conversion via ASC/CHR
• Character access via LEFT$, MID$ etc.
• Access to disk files via FILE.

Start BASIC with R BASIC. Lines starting with a number are taken as part of the program. You can correct a line by typing it again and delete a line by just typing its line numbers.

Lines not starting with a number are commands.

Files are not saved to disk unless you type SAVE. Both MONITOR and SYSTEM will return you to TOPS-10, the difference being that MONITOR will preserve core (see how jobs work) and SYSTEM does not.

As a demonstration, we'll run the the TPK algorithm. in BASIC. This uses the 4th edition version unchanged. I created the file on my PC and loaded it into my TOPS-10 account using the techniques described here. Then when I start BASIC I use the old command to read this from disk.

.r basic


READY, FOR HELP TYPE HELP.
old tpk

READY
list


TPK           15:36         07-MAR-79



100 REM TPK ALGORITHM IN BASIC
110 REM
120 DEF FNT(X) = SQR(ABS(X)) + 5*X**3
130 REM
140 REM MAIN PROGRAM
150 DIM A(11)
160 LET N=11
170 PRINT "PLEASE ENTER", N, "NUMBERS"
180 FOR I = 1 TO N
190 INPUT A(I)
200 NEXT I
210 PRINT "RESULTS ARE"
220 FOR J = 1 TO N
230 LET K = N - J + 1
240 LET R = FNT(A(K))
250 IF R > 400 THEN 280
260 PRINT R
270 GOTO 290
280 PRINT "TOO LARGE"
290 NEXT J
300 END

READY
run

TPK           15:36         06-MAR-79



PLEASE ENTER   11           NUMBERS
 ?10
 ?-1
 ?1
 ?2
 ?3
 ?4
 ?4.3
 ?4.305
 ?4.303
 ?4.302
 ?4.301
RESULTS ARE
 399.886
TOO LARGE
TOO LARGE
TOO LARGE
 399.609
 322
 136.732
 41.4142
 6
-4
TOO LARGE



TIME:  0.00 SECS.

READY

system

EXIT

.

Note that the line numbers in BASIC will not be recognised by TOPS-10 native commands as they expect 5 digit line numbers. However, the SOS editor has a /BASIC switch that does understand these so can be used to edit BASIC code outside of the interpreter.

There are a number of user contributed BASIC programs on the DECUS tapes (which were discussed briefly in the last article). Component 72 is a snapshot of the Dartmouth program library. Component 97 is a set of lessons for BASIC written in BASIC itself. Component 103 contains some mathematical routines in BASIC and Fortran.

Let's restore and run the teaching program in component 97 as an example. Looking at the trailing-edge page, component 97 will be on tape DECUS 10-LIB-1:

             DECUS 10-LIB-1                  5.64 Mbyte      902
      Contains 10-3 through 10-138           compressed   extracted
             except 10-101                   tape image     files

If you click on the extracted files link next to this you will see all files on the tape. Search on the page for 97.inf and you will see below that a set of BASIC files.

   1       25(7)  <007> 43,50014 31-Mar-75 dcus:[43,50141]97.inf
   12     1467(36) <007> 43,50014  9-Oct-70 dcus:[43,50141]tutr01.bas
    9     1099(36) <007> 43,50014  9-Oct-70 dcus:[43,50141]tutr02.bas
   11     1311(36) <007> 43,50014  9-Oct-70 dcus:[43,50141]tutr03.bas
   10     1202(36) <007> 43,50014  9-Oct-70 dcus:[43,50141]tutr04.bas
   11     1379(36) <007> 43,50014  9-Oct-70 dcus:[43,50141]tutr05.bas

Take a note of the user ID for this component - [43,50141].

On the previous page, download a copy of the compressed tape image and decompress it with bzip2 -d decuslib10-01.tap.bz2. Copy this under your simh directory, press Control-E on the console and attach the tape:

sim> at mta0 decuslib10-01.tap
%SIM-INFO: MTA0: Tape Image 'decuslib10-01.tap' scanned as SIMH format
sim> c

Login as the operator (user 1,2 password failsa) and restore the files using BACKUP. Here I'm going to put all the files in my home directory for user [200,200] but they can be placed anywhere you want.

.login 1,2
JOB 11 KA603 TTY1
Password: 
[LGNJSP Other jobs same PPN]
1100	22-Mar-79	Thur

.r backup
/tape mta0:
/restore dskb:[200,200]=dcus:[43,50141]*.*
!43,50141	DCUS

"Done

/^C

Note it will take about a minute to restore the files as the tape needs to be read sequentially.

Now switch over to your user account and run the newly restored program:

.r basic


READY, FOR HELP TYPE HELP.
old tutr01

READY
run

TUTR01        11:02         22-MAR-79



WELCOME TO TIMESHARING PDP-10.WE WILL
TRY TO TEACH YOU ENOUGH ABOUT THE SYSTEM IN THIS SITTING SO THAT
YOU WILL BE ABLE TO WRITE YOUR OWN COMPUTER PROGRAMS.

On Bitsavers, the 1974 BASIC Conversational Language Manual is probably the best guide for this version of BASIC. There's also 1968's Advanced BASIC for the PDP-10 from which the 1974 version looks to have been derived.

Both manuals draw material from Dartmouth's documentation (see their manual for a comparison). Interestingly, the 1968 DEC manual notes Dartmouth as the registered trademark holder of BASIC, and thanks them for using the material in their manual. The 1974 manual has no mention of BASIC being registered nor any acknowledgements to Dartmouth.

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.