The space shuttle primary computer system
Alfred Z. Spector, David Kenneth Gifford · Communications of the ACM · 1984
AS.How is the PASS coded and organized?Clemens.The software has an operating system written in assembler and applications written in HAL/S, a high-order language developed by Intermetrics, Inc., of Cambridge, Massachusetts.There are a number of stories about how the language was named--one is that it's from the computer in the movie 2001, although that is probably apocryphal.HAL/S is a real-time, structured engineering language that is very readable.Theoretically, at least, it should limit the amount of structure-induced errors because it makes the programmer pay attention to structure as the software is being developed.It's somewhat similar to PL/1.Macina.The operating system uses about 35K of the 106K 32-bit words available, and includes a prioritydriven process management scheme and the on-board display system software.Our process management scheme lets important processes run at the expense of lower priority processes if necessary.It is essentially a self-correcting system that off-loads low-priority processing when CPU demand is high. DG. What function does the PASS perform?Macina.You can divide the applications into three