The Scientific Data Systems Sigma 7


I worked on a Scientific Data Systems (SDS) Sigma 7 computer for about two years when I first came to Canada, at Computing Devices of Canada, just west of Ottawa. This was from 1968 to 1970. The company was purchased by Xerox in about 1970, and SDS became Xerox Data Systems, and the machine was then called the XDS Sigma 7.

The machine was a 32-bit processor, which was quite advanced for its time. It was reliable, but we had a fair amount of trouble with the operating system, which was quite new. The design was very clean and attractive to work with; much nicer than the very ugly instruction set and register configuration that still persists in IBM mainframes.

Much of the work we had to do was with real-time signal processing, and my job was to improve performance and make more memory available. I found an interesting solution, as the application made very little use of the operating system services once it was loaded, and the memory used by the OS was essentially wasted. So I used the OS as a laoder for the application, which then stripped out almost all the in-memory parts of the OS, and emulated the very few system calls that were actually needed. This was a fascinating project; the first one where I really had to understand interrupts and device control commands. It even worked - although I have no idea

Last updated : 2004-10-07