Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!wuarchive!udel!nigel.ee.udel.edu!mccalpin From: mccalpin@perelandra.cms.udel.edu (John D. McCalpin) Newsgroups: comp.arch Subject: Re: 64 bit addresses Message-ID: Date: 13 Feb 91 21:47:35 GMT References: <1991Feb13.212041.14368@news.arc.nasa.gov> Sender: usenet@ee.udel.edu Organization: College of Marine Studies, U. Del. Lines: 22 Nntp-Posting-Host: perelandra.cms.udel.edu In-reply-to: lamaster@pioneer.arc.nasa.gov's message of 13 Feb 91 21:20:41 GMT >On 13 Feb 91 21:20:41 GMT,lamaster@pioneer.arc.nasa.gov (Hugh LaMaster) said: Hugh> (The Cyber 205 used to have 64 bit "addresses" (actually Hugh> descriptors). Regardless of whatever other problems the machine Hugh> had, the addresses were not a problem. I note that, though, it Hugh> only had to do integer arithmetic on 48 bits of the address, not Hugh> 64.) To clarify, the Cyber 205 used 48-bit *bit* addresses. Since almost all addressing was actually done by 64-bit words, the last 6 bits were almost invariably 0. Still, 42 bits of word addressing was found to be adequate for most programs. (This equals 45 bits of byte addressing). The upper 16 bits were used to store the vector length for vector instructions. Integer instructions operated only on the lower 48 bits. Although 48-bit addresses would probably handle most applications for the next few years, the approach taken by the 205 was not RISCy, to say the least! -- John D. McCalpin mccalpin@perelandra.cms.udel.edu Assistant Professor mccalpin@brahms.udel.edu College of Marine Studies, U. Del. J.MCCALPIN/OMNET