Download the Windows zip file from the dtss.dartmouth.edu site and unpack it to a directory. Then just run the DTSS.EXE program to start; on non-Windows devices with Wine installed, run wine DTSS.EXE instead.

There are no user configurable options to adjust the simulator or interface.

Input should all be in upper case. Note that copy/paste does not work, usually bringing up an error message that ends the emulator. But there is a way to get programs in and out of the system - see below.

Type NEW HELLO to start a new program called HELLO. Then type the program lines including the starting line number.

10 FOR I = 1 TO 5
20 PRINT "HELLO, WORLD"
30 NEXT I
40 END

You can edit the program by retyping any lines. To delete a line, just type the line number and press Enter.

Type RUN to start the program and LIST to get a listing.

To save the program to disk, type SAVE.

You can then exit the emulator by typing BYE or just closing the window. When you come back, load your old program by typing OLD HELLO.

There are two libraries, a personal one and a system one. Type CAT to see your library: you will see your HELLO program along with a number of other demo programs.

To see what is in the system library, type OLD LIBCAT*** then LIST. To load one of these programs, for example FTBALL, type OLD FTBALL*** (note the *** at the end to denote a system program.

100 BASIC PROGRAMS
110 
120 AVELOG***   AVERAGE OF 100 LOGARITHMS
130 FTBALL***   DARTMOUTH FOOTBALL
140 GUESS***    GUESS A NUMBER FROM 1 TO 100
150 GCD***      GREATEST COMMON DIVISOR (GCD)
160 GCD3NO***   GCD OF THREE NUMBERS
170 MORT***     CALCULATES LIFE OF A MORTGAGE
180 NORMAL***   PLOT OF THE NORMAL CURVE
190 QUAD***     SOLVE A QUADRATIC EQUATION
200 PIE***      APPROXIMATE PIE

Programs are stored on the host file system as plain text files, with your library in the same dierctory as the executable, and the system library under LIB/. So to see the text of your HELLO program, look for the file named HELLO without an extension.

You can view, edit and create new files outside of the emulator using this method. Remember to save files in DOS format, ie with CR/LF at the end of each line.

The SPEED command will adjust the speed of the emulator: SPEED 10 is approximately the speed of the original system.

You can switch from BASIC to ALGOL with SYSTEM ALGOL.

There is a computer aided learning system called TEACH available also.

The DTSS emulator zip file contains three useful documents.

• Commands.pdf
• A BASIC Outline.pdf
• An Algol Outline.pdf

A 1964 introduction to the system and BASIC can be found on bitsavers.

We'll look at BASIC and ALGOL in more detail in upcoming posts.

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.

There are code listings for the GE-235 and D-30 executives along with BASIC and ALGOL compilers from about 1965 available on dtss.dartmouth.edu, but sadly later versions of DTSS or the libraries of user code have not been found.

Bitsavers has manuals from Dartmouth for DTSS/BASIC/ALGOL and from Honeywell for the hardware.

Lars Brinkhoff has collected known DTSS material, including all the above, at Github.

A group of people from Dartmouth, including Thomas Kurtz, came together in the early 2000s to scan the listings, create an assembler and build a simulator (written in True BASIC). This only simulates the GE-235 part of the system, so is not multi-user, but can run BASIC and ALGOL code. Only 32 bit Windows and classic Mac binaries are available, however the former runs fine under Wine.

There was also a web based emulator of the GE-235 and D-30 running similar era code but including the multi-user executive. Although the website is still online, as of 2025 logins no longer works and I have not been able to find a contact address for the owners.

We will use the Windows emulator dtss.exe to explore DTSS further.

• A quick tour using dtss.exe
• DTSS architecture
• BASIC
• Algol

June 2025: correct name for Dartmouth College, clarified use of GE-225 vs 235.

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.

Note that QED only supports 6- and 12-bit line-marked files and ASCII files, not card image files. If your file is in card image format, convert it using SQUASH first.

QED has the concept of multiple buffers rather than working on a single file at a time. In the below I start QED and read in TPK MAD to the default buffer using the r command with the s option to mean 6-bit line-marked.

qed
W 1755.3
QED     
rs tpk mad

x will list the buffers in use: here we have the default buffer 0 with 23 lines:

x
"0" 0023

The p command prints lines from the buffer. Like many commands, it takes an optional range as its first argument. Without a range it defaults to . which is the current line, but I can specify line numbers or ranges of lines:

p                        
           END OF PROGRAM
10 p                     
           DIMENSION NUM(11)
3,5 p                       
           INTERNAL FUNCTION(X)
           ENTRY TO F.         
           FUNCTION RETURN SQRT.(.ABS.X) + 5 * X.P.3

1,$ p would print all lines of the file.

Range arguments can also be regular expressions enclosed in ~/~s.

/th.* input/,/read/ p            
           THROUGH INPUT,FOR J=0,1,J.GE.N
INPUT      READ FORMAT FMT,NUM(J)

Had we used the d command instead of p, it would delete those three lines.

gp/11/
           N = 11
           DIMENSION NUM(11)
           PRINT COMMENT $PLEASE ENTER 11 NUMBERS$

1,$ s/11/15/

/other/                  
           OTHERWISE
i                   
           PRINT COMMENT $TRY AGAIN$
\f

/internal func/,/end of func/ m1

b1                       
1,$p
           INTERNAL FUNCTION(X)
           ENTRY TO F.         
           FUNCTION RETURN SQRT.(.ABS.X) + 5 * X.P.3
           END OF FUNCTION                          
/internal/
           INTERNAL FUNCTION(X)
s/int/ext/                     
p
           EXTERNAL FUNCTION(X)

ws func mad

b0                        
/sqrt/
?1

ws tpk mad

b2                       
i
mad tpk
\f

b0
e2
LENGTH 00152.  TV SIZE 00006.  ENTRY 00040

• f will replace the contents of the current buffer with information such as date, time, login details etc.
• k will sort a range
• l will list a file to the console
• u - the audit command - will create a buffer showing the effect of all edits done since the last read.

QED is described more fully in the CTSS Programmer's Guide section AH.3.09 p353.

Source code for QED on a number of different systems is collected on Github at arnoldrobbins/qed-archive.

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 if needed.

TYPSET is an editor where you can add and change text, including control codes to specify output formatting. This uses the same editor commands as EDC and EDL (in fact, as described in an earlier article, the design for these editors came from TYPSET; see that article for how to use the editor).

TYPSET expects the name2 of a file to be (MEMO), so the command TYPSET abc will create or edit a file ABC (MEMO). It uses 12-bit line-marked files, so with a suitable typewriter you could enter lower case and an extended range of symbols. If you are using a recent version of s709/ctss-kit or my quickstart or eliza-ctss released after 22 May 2025 this will support it as well.

Control words always start with a . (dot) in column 1. There are full and abbreviated forms, eg .center, which will center the next line, can be abbreviated as .ce.

A full list of control words:

As the output for this system was a typewriter, there was obviously no concept of bold, italics, different fonts, text size etc. One feature the typewriter did have that we don't have today was backspacing. For example, to get something like Ç you could enter C, then backspace, then ,. The system will move the head back one character on backspace so the two symbols print in the same space.

The RUNOFF command takes the input memo file, interprets the control words and prints the formatted output to the typewriter console. It prompts the user LOAD PAPER, HIT RETURN so the paper can be changed if needed.

As an example, the screenshot above was produced by this file:

.ll 80
.ds
.header TIMERESHARED.COM
.hm center
.bp
.center
CTSS: Document production with TYPSET and RUNOFF

The concept of using computers to produce documents was first
demonstrated before CTSS in 1960 with the Colossal Typewriter project
on the PDP-1. Rather than typing directly to paper, you could store
text and edit it in memory before printing to a typewriter or line
printer. However, in single user mode, it was not a cost-efficient use
of a computer, as alluded to by a similar PDP-1 project Expensive
Typewriter.

TYPSET/RUNOFF are described more fully in the CTSS Programmer's Guide section AH.9.01 p504; there's an OCR'd version at multicians.org.

These commands was the inspiration for similar text production systems on Multics and Unix. On a Unix system today you are likely to find troff which uses very similar control words.

May 2025: Updated to point to the newer versions of the s709 emulator/ctss-kit for full support of lower case letters. Thanks to Dave Pitts for his continued work on this system.

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.