Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!pyramid!prls!mips!mash From: mash@mips.COM (John Mashey) Newsgroups: comp.arch Subject: RPM-40 (clarification) Message-ID: <1728@winchester.mips.COM> Date: 1 Mar 88 08:25:24 GMT References: <9679@steinmetz.steinmetz.UUCP> <9689@steinmetz.steinmetz.UUCP> <1695@winchester.mips.COM> Reply-To: mash@winchester.UUCP (John Mashey) Organization: MIPS Computer Systems, Sunnyvale, CA Lines: 36 Keywords: DAIS, 14 MIPS, General Electric In article <1695@winchester.mips.COM> I wrote: ... >I assume this must be humorous: it is obvious that this architecture was >designed to be a microcontroller, to run limited-size, embedded, >and definitely, non-UNIX applications. It seems OK for that purpose, >but it obviously wasn't built for running UNIX or large applications >(and there's nothing wrong with that). I probably should have said more: I've gotten several mailings wondering why it is obvious ("This is Fermat's Last Theorem; the proof is left to the student as an exercise..." :-) and urging me to post more, so: The reasons were, in order of impact: 1) (architecture, critical) The MMU isn't appropriate for UNIX. 2) (fuzzy boundary between architecture and implementation, could be fixed, but probably with performance hit, and certainly with substantial redesign of bus interface, and maybe coprocessor interface). According to the information made available so far, the design treats the 128K of memory as THE memory, not as caches. If the size is limited by the number of SRAM chips that can be driven directly, the size limit grows with time, but is fairly small in comparison to that needed by workstations these days. ------------ 3) (architectural, but not critical) Performance tunings: these are NOT critical, in that they could still let you have a workstation with an RPM-40 as currently implemented. However, some of the design tradeoffs seem tuned in directions opposite those of programs found in general-purpose environments. (As appropriate, remember that they said it was for embedded environments.) -- -john mashey DISCLAIMER: UUCP: {ames,decwrl,prls,pyramid}!mips!mash OR mash@mips.com DDD: 408-991-0253 or 408-720-1700, x253 USPS: MIPS Computer Systems, 930 E. Arques, Sunnyvale, CA 94086