SDS 940
| Type | Mainframe computer |
|---|---|
| Units sold | 60 |
| Operating system | Berkeley Timesharing System |
| CPU | Integrated circuits based custom 24-bit CPU |
| Memory | 16 and 64 kilowords of 24 bits + parity, additional 4.5 MByte swap |
| Storage | 96 MByte at 117 kByte/s, access time 85 ms |
| Graphics | Instructions of beam motion, character writing, etc, 20 characters per second. 1000 character terminals with 875 line screen. |
| Connectivity | Paper tape, line printer, modem |
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 Stanford Research Institute "oN-Line System" (NLS) was demonstrated on the system.
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 as part of their Project Genie that ran between 1964 and 1965. Genie added memory management and controller logic to an existing SDS 930 computer to give it page-mapped 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. Words were 24 bits plus a parity bit. 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 16 384 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.
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