Path: utzoo!news-server.csri.toronto.edu!rutgers!usc!elroy.jpl.nasa.gov!decwrl!atha!mips!mash From: mash@mips.com (John Mashey) Newsgroups: comp.arch Subject: 48-bit computers Message-ID: <666@spim.mips.COM> Date: 3 Mar 91 20:45:56 GMT Sender: news@mips.COM Organization: MIPS Computer Systems, Inc. Lines: 33 Nntp-Posting-Host: winchester.mips.com Various people asked about the existence of 48-bit computers. I don't know of any, offhand that are being sold today. Ones sold in the past include: 1) Honeywell 800, 400, 1400-1800 2) CDC 1604, 1604A, 3[468]000 (the 3[1235]00 were 24-bitters) 3) English Electric KDF9 4) Burrounghs B5000, B5500, D825, B8500 One person asked about current Unisys (Burroughs) A-series. Correct me if I'm wrong, but I think these are derived from the Burroughs B6500/B7500 mainframes, which were the successors to the B5500 & friends, and they used 51 bits. 51 bits? Yes. The 48-bit words of the B5000 used up to the top 3 bits as flag bits, i.e., bit0 == 0 said rest of 47 bits were numeric operand. bit1 == 1 said rest of word was something else, separated by bit2. In the B6500 and later, they added 3 more bits for tags, which seemed to me to be cleaner, as it left the fairly clean number 48. The 48--bit machines look to me to be a late-50s, 1960s mainframe & mid-range phenomenon that has since died off. REFERENCE: Bell & Newell, COMPUTER STRUCTURES: READINGS AND EXAMPLES, McGraw-Hill, New York, 1971. -- -john mashey DISCLAIMER: UUCP: mash@mips.com OR {ames,decwrl,prls,pyramid}!mips!mash DDD: 408-524-7015, 524-8253 or (main number) 408-720-1700 USPS: MIPS Computer Systems MS 1/05, 930 E. Arques, Sunnyvale, CA 94086