A good starting reference to many of the computers used in spaceflight is NASA Contractor Report 182505 Computers in Spaceflight The NASA Experience James E. Tomayko Wichita State University Wichita, Kansas It's available in hardcopy from CASI, and over the web from http://www.hq.nasa.gov/office/pao/History/computers/Compspace.html It gives a decent overview of the hardware involved, and has references to very technical documents if you want to go into that much detail. The HAL/S programming language is covered as an appendix. -- Tim Shoppa Email: shoppa(a)trailing-edge.com Trailing Edge Technology WWW: http://www.trailing-edge.com/ 7328 Bradley Blvd Voice: 301-767-5917 Bethesda, MD, USA 20817 Fax: 301-767-5927