SDS 940

SDS 940

The SDS 940 was Scientific Data Systems' (SDS) first machine designed to support time sharing directly, and was based on the SDS 930's 24-bit CPU built primarily of integrated circuits. It was announced in February 1966 and shipped in April, becoming a major part of Tymshare's expansion during the 1960s. The influential SRI "oN-Line System" (NLS) was based around SDS 940 hardware.

After SDS was acquired by Xerox in 1969 and became Xerox Data Systems, the SDS 940 was renamed as the XDS 940.

The design was originally created by the University of California, Berkeley, along with Tymshare, as part of their Project Genie that ran between 1964 and 1965. Genie added memory and controller logic to an existing SDS 930 computer to give it paged virtual memory, which would be heavily copied by other designs. The 940 was simply a commercialized version of the Genie design, and remained backwardly compatible with their earlier models (with the exception of the 12-bit SDS 92).

Like most systems of the era, the machine was built with a bank of core memory as the primary storage, allowing between 16 and 64 kilowords. This was backed up by a variety of secondary storage devices, including a 1376 kWord drum in Genie, or hard disks in the SDS models in the form of a drum-like 2097 kWord "fixed head" disk or a 16777 kWord traditional "floating head" model. The SDS machines also included a paper tape punch and reader, line printer, and a real-time clock. They bootstrapped from paper tape.

oftware System

As of 1969, the XDS 940 Software System consisted of the following:
* Time-Sharing Monitor
* Time-Sharing Executive

The minimum configuration required to run the Software System included (partial list):
* Two 16K-word core memory modules (with multiple access)
* Two rapid-access disc (RAD) storage units and couplers (just under 4M character capacity each); optionally two more could be connected
* Disc file and coupler, with 67M characters of storage
* Magnetic tape control unit and two magnetic tape transports (controller supports up to 8)
* Asynchronous communication controller(s), supporting up to 64 teletypewriter lines each

Additional software was available from the XDS Users' Group Library, such as a string processing system, "SYSPOPs" (system programmed operators, which allow access to system services), CAL (Conversational Algebraic Language, a dialect of JOSS), QED (text editor) (a text editor), TAP (Time-sharing Assembly Program, an assembler), and DDT, a debugging tool.

Notable installations

A San Francisco counterculture community action group called "Project One" used a free surplus XDS 940 as described in Rolling Stone magazine in 1972.

ee also

*Berkeley Timesharing System


*Xerox Data Systems, "XDS 940 Computer" (1969)
*Rolling Stone, "Spacewar", 7 December 1972, loacated at

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