Editing Scientific Data Systems (section)

===Sigma series===
[[File:LCM - Xerox Sigma 9 (right) and related equipment - 01.jpg|thumb|An XDS Sigma 9 at the [[Living Computer Museum]], Seattle, Washington, 2014]]
In December 1966 SDS shipped the entirely new [[SDS Sigma series|Sigma series]], starting with the [[16-bit]] Sigma 2 and the [[32-bit]] Sigma 7, both using common hardware internally. The success of the [[IBM System/360]] and the rise of the 7-bit [[ASCII]] character standard was pushing all vendors to the 8-bit standard from their earlier 6-bit ones. SDS was one of the first companies to offer a machine intended as an alternative to the IBM System/360; although not compatible with the 360, it used similar data formats, the EBCDIC character code, and in other ways, such as its use of multiple [[processor register|registers]] rather than an [[Accumulator (computing)|accumulator]], it was designed to have specifications that were comparable to those of the 360.

Various versions of the Sigma 7 followed, including the cut-down Sigma 5 and re-designed Sigma 6. The Xerox Sigma 9 was a major re-design with instruction lookahead and other advanced features, while the Sigma 8 and Sigma 9 mod 3 were low-end machines offered as a migration path for the Sigma 5. The French company [[Groupe Bull|CII]], as a licensee of SDS, sold about 60 Sigma 7 machines in Europe, and developed an upgrade with [[virtual memory]] and [[Multiprocessing|dual-processor]] capability, the [[Iris 80]]. CII also manufactured and sold some 160 Sigma 2 systems.

The Sigma range was very successful in the niche real-time processing field, due to the sophisticated [[hardware interrupt]] structure and independent I/O processor. The first node of [[ARPANET]] was established by [[Leonard Kleinrock]] at [[UCLA]] with an SDS Sigma 7 system.