GE-200 Series Time-Sharing System (DTSS) – INTERIM COMPUTER MUSEUM

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INTERIM COMPUTER MUSEUM<br>Hardware/Software Preservation and Restoration Stories

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Check out DTSS Reanimated in our Vintage Remote Systems.

There is a particular kind of loss that haunts computing history. It is not the loss of a machine, machines can be found, restored, coaxed back to life by people patient enough to chase a cold solder joint for three days. It is the loss of a running system: the software, the operating environment, the feel of sitting down and having the thing answer you. Hardware can survive in a warehouse for fifty years. A working system can evaporate in five, when the last platform that ran it stops booting.

The Dartmouth Time-Sharing System is one of the most important running systems ever built, and it came very close to that second kind of loss. At the Interim Computer Museum it is now running again. Here is how it got there.

An idea at Dartmouth, built with GE

In the early 1960s, using a computer meant handing a deck of punched cards to an operator and waiting. John Kemeny and Thomas Kurtz, two mathematicians at Dartmouth, thought ordinary undergraduates should instead be able to sit down at a terminal and use a machine directly, while they were still thinking. Making that real took two inventions at once: a way for many people to share one computer, and a language a beginner could actually learn. The language was BASIC. The system that hosted it was DTSS, and it first ran in 1964. It was not the first time-sharing system – Fernando Corbató’s CTSS was running at MIT by 1961, building on an idea John McCarthy had floated at the end of the 1950s – but those systems were built by and for computer specialists. DTSS was the first built for the novice in the chair: a system whose whole reason for being was to let people who were not programmers sit down and use a computer directly, while they were still thinking.

The hardware came from General Electric, and the design was genuinely clever. Rather than make one computer do everything, Kurtz and Kemeny used two. A GE-235 executed the programs – your BASIC, your ALGOL. A separate GE DATANET-30 (the DN-30) handled all the communications with the teletypes and scheduled work onto the 235. GE sold that paired configuration as the GE-265, the model numbers added together. This was the original DTSS, later called Phase I, and it ran from 1964 to around 1967.

GE takes it to market

GE was already selling idle time on the computers it used for customer demonstrations, and it recognized what it had. By the mid-1960s the company was offering the Dartmouth system commercially as the GE-200 Series Time-Sharing System, on that same paired GE-235 and DATANET-30 hardware it sold as the GE-265. The reference manual for that service, dated September 1967, describes a system a Dartmouth undergraduate would have recognized on sight. A user dials in; the DATANET-30 answers the line and runs the HELLO sequence, checking the caller’s user number against the terminals accredited to use it. Once admitted, the user names a system and goes to work, and when a RUN or EDIT is issued the front end hands the job to the GE-235 through a shared area the manual calls the "Mailbox" passing along the user number, the program name, and the chosen system. The systems on offer were exactly the Dartmouth ones: BASIC, EDIT, FORTRAN, and an ALGOL that GE’s own companion manual names, without euphemism, "Dartmouth ALGOL."

What GE put on the market, in other words, was not merely modeled on Dartmouth, it was the Dartmouth system, the two-computer design and the conversational BASIC and all, sold under a GE catalog number. For the first time a business or a school anywhere with a teletype and a phone line could dial into a friendly, BASIC-speaking computer and be answered in seconds. The system spread across the country as the first widely available taste of interactive computing.

GE eventually took its own commercial line down a separate path on the larger 36-bit GE-635 – the Mark II and Mark III services, on a different operating system, which over the years grew into the consumer network GEnie. But the thing that put interactive computing in front of people in the mid-1960s, and the thing this story is about, was that original Dartmouth system: Phase I, the GE-235 and the DATANET-30.

A Teletype model ASR33 in Seattle

By 1968 the GE service had spread far enough to turn up in a boys’ prep school two thousand miles from Hanover. That spring, a Lakeside School teacher named Bill Dougall persuaded the Lakeside Mothers’ Club to spend the proceeds of its annual rummage sale, about $3,000, on a Teletype Model 33 and a block of time on a General Electric time-sharing system, the commercial descendant of the Dartmouth design. The machine was not part of the curriculum. It sat in a room and answered whoever sat down at it, over a phone line, in seconds. Two of the students who could...