Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/17/84; site opus.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!hao!nbires!opus!rcd From: rcd@opus.UUCP (Dick Dunn) Newsgroups: net.arch Subject: Re: Why Virtual Memory Message-ID: <178@opus.UUCP> Date: Wed, 30-Oct-85 02:08:42 EST Article-I.D.: opus.178 Posted: Wed Oct 30 02:08:42 1985 Date-Received: Fri, 1-Nov-85 03:10:27 EST References: <480@seismo.CSS.GOV> <384@unc.unc.UUCP> Organization: NBI,Inc, Boulder CO Lines: 22 > It is interesting to note that 10 years ago or so, all large systems > had virtual memory whereas small systems did not. > > Now the largest systems (e.g., Cray 2) do not have virtual memory, > whereas it is more and more common for small systems ("microprocessors", > and I use the term in quotes) to have virtual memory. If you mean by "virtual memory" something like paging capability--or in particular, hardware support for a logical address space larger than the physical address space, it is NOT true that all large systems had virtual memory 10 years ago. The Cray 2 is not markedly different with respect to memory address mapping than the Cray 1, the CDC 7600, or the CDC 6600--each the fastest commercial machine of its day. The 6600 takes us back about 20 years. Quite simply, in machines as large as these, you cannot pretend that you have memory that isn't really there, for the class of problem they tend to be used to solve. -- Dick Dunn {hao,ucbvax,allegra}!nbires!rcd (303)444-5710 x3086 ...At last it's the real thing...or close enough to pretend.