SDS Sigma series

The SDS Sigma series from SDS was a family of two lines of computers; 16-bit and 32-bit (see below), each mostly program compatible among members of that line. They were intended for use partially or wholly in real-time settings, but also provided batch processing facilities (also time-sharing, on the 32-bit systems). This dual capability was described as "multi-use" in SDS' marketing material.

The Sigma 6, 8 and 9 members were all produced after the merger of SDS and Xerox (forming 'Xerox Data Systems', 'XDS') in March 1969. Xerox later sold XDS to Honeywell, in 1975; Honeywell briefly continued support of the Sigmas, but then terminated it. At that point, other companies, including Telefile, Ilene Industries Data Systems, and Realtime Computer Equipment started to build and sell their own program compatible machines.

A Sigma 7 at UCLA was the first computer connected to the nascent ARPANET.

Family members

As mentioned, there were two groups (lines) of program compatible machines; a 16-bit group and a 32-bit group. All used a load-store architecture.

Below are thumbnail descriptions of the models in the Sigma family, in the order of their dates of introduction.

16-bit group

Their instruction set includes 'memory reference' instructions:

Opcode				R	I	X	S	Displacement
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

• R - Self-relative
• I - Indirect
• X - Indexed
• S - Base-relative

There are also 'copy' instructions (register-to-register operations) and conditional branch instructions.

Sigma 2

First member of the of the Sigma 16-bit group; introduced in 1966.

Sigma 3

Introduced in 1969.

32-bit group

Their instruction set is also principally 'memory reference' instructions:

I	Opcode							R				X			Address
00	01	02	03	04	05	07	07	08	09	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31

• I - Indirect
• R - Register (in current register block)
• X - Index register (ditto)

Again, there are also conditional branch instructions. Like the PDP-10, references to the low 16. main memory locations automagically turn into references to the corresponding register; memory reference instructions thus provide a complete set of register-to-register operations (definitely on the 7 and 5; not confirmed on the others).

Sigma 7

First member of the of the Sigma 32-bit group; announced in April, 1966.

Sigma 5

Introduced in 1967; a reduced-cost version, without separate input/output processors.

Sigma 6

Announced in May, 1970; SDS' initial entry into commercial business data processing.

Sigma 9

Announced in October 1970.

Sigma 8

Introduced in 1972.

Software

The Sigma series came with a fairly complete suite of software, which included a slew of operating systems: Basic Control Monitor (BCM) and Real-Time Batch Monitor (RBM) for the 16-bit line; and for the 32-bit machines, Basic Control Monitor, Batch Time-Sharing Monitor (BTM; a descendant of the Batch Processing Monitor, BPM), Control Program-Five (CP-V) (a successor to the Universal Timesharing System (UTS)), and Control Program for Real-Time (CP-R).

Programming languages available included FORTRAN IV, COBOL, LISP 1.5, BASIC, and APL, as well as the Symbol, Meta-Symbol and Extended Symbol assemblers.

Outside SDS, the Lawrence Livermore Laboratory made their own operating system called GORDO. UCLA took GORDO and developed it further; they named the result SEX.

External links

• sigma - documentation on Bitsavers
  • Sigma CPUs
• The Sigma Family - sales brochure; pre-dates the Xerox merger
• Guide to the Keith G. Calkins collection on Sigma systems
• The SDS Sigma 7: A Real-Time Time-Sharing Computer
• The Computer That Will Not Die: The SDS Sigma 7 Narrator: it died.
• 3420 Boelter Hall: Where It All Began - UCLA Internet Museum, displaying a Sigma 7 front panel