An SDS 930 system consisted of at least three standard (30 cu. ft.) cabinets, comprising the arithmetic and logic unit, at least 8,192 words (24-bit + simple parity bit) magnetic core memory, and the IO unit. Two's complement integer arithmetic was used. The machine had integer multiply and divide, but no floating point hardware. An optional correlation and filtering unit (CFE) could be added, which was capable of very fast floating point multiply-add operations (primarily intended for digital signal processing applications).
A free-standing console was also provided, which included binary displays of the machine's registers and switches to boot and debug programs. User input was by a Teletype Model 35 ASR unit and a high-speed paper tape reader (300 cps). Most systems included at least two magnetic tape drives, operating at up to 75 inches/second at 800 bpi. The normal variety of peripherals was also available, including magnetic drum units, card readers and punches, and an extensive set of analog-digital/digital-analog conversion devices. A (vector mode) graphic display unit was also available, but it did not include a means of keyboard input.
The SDS 930 was a typical small to medium scale scientific computer at the time. Speed was good for its cost, but with an integer add time of 3.5 microseconds, it was not in the same league as the scientific workhorses of the day (the CDC 6600, for example). A well equipped 930 could easily exceed 10 cabinets and require a 300-500 sq. ft. climate controlled room. The price of such a system in 1966 would be in the neighborhood of $500K.
Programming languages available included FORTRAN II, ALGOL 60, and the assembly language known as Metasymbol. The FORTRAN system was very compact, having been designed and implemented by Digitek for SDS to compile and run in 4,096 word SDS 900 series machines. To do anything useful in such small memory space, the compiler relied on an SDS architectural feature known as Programmed OPeratorS, or POPS. This feature consisted of a single bit in the instruction word that caused the machine to "mark place and branch" to the memory address of the instruction code value plus 100 (octal). As a result, pseudo instructions could be defined and implemented yielding very compact special-purpose code. Both the FORTRAN compiler and runtime took advantage of this capability.
Towards the end of the SDS 930's market lifetime a real-time operating system was introduced, and it included a FORTRAN IV compiler. Neither the operating system nor the compiler were used heavily by customers. Many organizations modified and enhanced the 930's hardware. Project Genie at the University of California, Berkeley, added hardware to permit time-sharing with the Berkeley Timesharing System. These changes later formed the basis for the SDS 940. Other operating systems were also written for the machine by customers, including Arachnid (Spider) at the University of Texas at Austin.
SDS 930s could be found at most of the major US government labs at the time, including Los Alamos Scientific Laboratory. Early Flight simulators used the SDS 930, because of its hardware integer multiply and divide capability and its real-time data acquisition and control peripheral modules. The machines were particularly well-suited to this and other kinds of data acquisition and real-time analysis, as well as to serving as a digital control system for analog-hybrid systems.
By 1974 estimates, there were about 200 SDS-930/940/945 computers still installed.
- Keith G. Calkins (June 1984). "The COMPUTER That Will Not Die: The SDS SIGMA 7". 5th TeleExchange Proceedings. Orlando, Florida. Retrieved April 21, 2011.
- SDS 930 Computer Reference Manual (PDF). SDS 90 00 64F (Scientific Data Systems). November 1969.
- A programmed operator was a hardware concept on the SDS 900 series of computers similar to the concept of the Atlas computer's "extracodes". The programmed operator calling mechanism allowed computer operation codes to be interpreted by software code. See Scientific Data Systems, "SDS 900 Series", technical manual. Cf. Programmed Operator. Also see "SDS 910 Reference Manual", February 1970. Cf. Appendix E. page A-19, "Programmed Operators" for an in-depth discussion of Programmed Operators.
- Bell, Gordon, "Computer Structures: Readings and Examples", Section 6: Processors with multiprogramming ability, p.275. "The [SDS] 940 uses a memory map which is almost a subset of that of Atlas but is more modest than that of the IBM 360/67 [Arden et al., 1966] and GE 645 [Dennis, 1965; Daley and Dennis, 1968]. A number of instructions are apparently built in via the programmed operator calling mechanism, based on Atlas extracodes (Chap. 23). The software-defined instructions emphasize the need for hardware features. For example, floating-point arithmetic is needed when several computer-bound programs are run. The SDS 945 is a successor to the 940, with slightly increased capability but at a lower cost."