SDS Sigma-5

SDS Sigma-5 was a 32-bit computer that was introduced by the Xerox company in 1965. (Scientific Data Systems [SDS] was a company Xerox had acquired in 1969.) This was a reduced-capability version of the Sigma 7 computer. It was commercially retired in the 1970s after Xerox left the Mainframe computer manufacturing business.

The computers sold for US$300,000 with 16 kilobytes of random-access memory, with an optional memory upgrade to 32 kb for an additional $50,000. The hard disk drive had a capacity of 3 megabytes. [cite news
first=Byron | last=Spice
title=Saying goodbye to the Sigma 5
publisher=Pittsburg Post-Gazette
date=October 01, 2001
url=http://www.postgazette.com/healthscience/20011001sigma1001p5.asp
accessdate=2007-08-15 ]

The Sigma-5 computer owned by Carnegie Mellon University was donated to the Computer History Museum in 2002. The system consisted of five full-size cabinets with a monitor, control panel and a printer. It is possibly the last surviving Sigma-5 that is still operational.cite news
title=Carnegie Mellon’s Sigma-5 Retires After 30 Years of Service
publisher=Carnegie Mellon University
date=June 2002
url=http://www.chem.cmu.edu/about/news/about-news-200206-sigma.html
accessdate=2007-08-15 ]

Memory size increments for all SDS/XDS/Xerox computers was stated in kWords, not kBytes. The Sigma 5 base memory was 16K 32-Bit words (64K Bytes). Maximum memory was limited by the length of the instruction address field of 17 bits, or 128K Words (512K Bytes). Although this is a trivial amount of memory in today's Intel based technology, Sigma systems performed their tasks exceptionally well, and few were deployed, or needed, the maximum 128K Word memory size.

The primary difference between the Sigma 5 and Sigma 7 are the Sigma 5 included an integral IOP (but most systems deployed actually used the same external Multi-plexing IOP as the Sigma 7), and the Sigma 7 supported a Floating Point Arithmetic unit and a broader set of complex instructions useful for data interpretation (Interpret, Analyze, etc;) and virtual memory mapping capabilities. Otherwise, they were virtually identical and the Sigma 5 was deployed in far greater numbers.

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