SDS 940
The SDS 940 was Scientific Data Systems' (SDS) first machine designed to directly support time-sharing. The 940 was based on the SDS 930's 24-bit CPU, with additional circuitry to provide protected memory and virtual memory. 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. This machine was later used to run Community Memory, the first bulletin board system. After SDS was acquired by Xerox in 1969 and became Xerox  Data Systems, the SDS 940 was renamed as the XDS 940. History. The design was originally created by the University of California, Berkeley as part of their Project Genie that ran between 1964 and 1969. 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 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. A file storage of 96 MB were also attached . The line printer used was a Potter Model HSP-3502 chain printer with 96 printing characters and a speed of about 230 lines per minute. Software system. The operating system developed at Project Genie was the Berkeley Timesharing System. By August 1968 a version 2.0 was announced that was just called the "SDS 940 Time-Sharing System". As of 1969, the XDS 940 software system consisted of the following: The minimal configuration required to run the Software System included (partial list): 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 (a text editor), TAP (Time-sharing Assembly Program, an assembler), and DDT, a debugging tool. A cathode-ray tube display with 26 lines that operated DDT loader-debugger that were originally designed to operate from a teletype terminal were also available. Notable installations. Butler Lampson estimated that about 60 of the machines were sold.