Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!ut-sally!utah-cs!utah-gr!stride!stride1!mitch From: mitch@stride1.UUCP (Thomas P. Mitchell) Newsgroups: comp.arch,comp.sys.nsc.32k,comp.sys.intel,comp.sys.m68k Subject: Re: Question: on-chip or off-chip MMU? Message-ID: <665@stride.Stride.COM> Date: Fri, 8-May-87 20:13:25 EDT Article-I.D.: stride.665 Posted: Fri May 8 20:13:25 1987 Date-Received: Sun, 10-May-87 01:04:05 EDT References: <5635@shemp.UCLA.EDU> <122@motsj1.UUCP> Sender: news@stride.Stride.COM Reply-To: mitch@stride1.UUCP (Thomas P. Mitchell) Organization: MicroSage Comp. Sys. Inc., 680 S. Rock Blvd, Reno, NV 89502 Lines: 37 Xref: mnetor comp.arch:1229 comp.sys.nsc.32k:143 comp.sys.intel:230 comp.sys.m68k:464 In article <122@motsj1.UUCP> rich@motsj1.UUCP (Rich Goss) writes: >In article <5635@shemp.UCLA.EDU> fan@CS.UCLA.EDU (Roy Fan) writes: >>-------------- >> I am doing a project on MMU's, and from reading various uP >>data books, I have several questions: >> >> Question 1 : are there any other factors that might affect the >>design of the MMU being on-chip or off-chip? The answer is system design, what functions do you want your customers to put arround your processor and what will they do with them. Also what the programmers model looks like. I was lucky enough to hear a short talk by a gentleman at MIPS. He outlined some of their design goals. Memory translation takes time in fact a lot of time. Their reduced instruction set gave them enough silicon to build the kind of processor that they felt Unix needed. When the 8080 was born UNIX was a rare beast. So clearly Intel did not have the Unix community in their system design goals. You might also look at a patent by Sun on their MMU it gives a clue toward the problems with time when building an MMU. (We use 68010 and 68020s here). >> >> Question 2 : if there is enough space on the chip, would >>everybody put the MMU on-chip? If there was enough space everything would be on chip. Gate delay times are much shorter on chip than off chip. Low_Power + CPU + MMU + 100 GB RAM = ;-). Thomas P. Mitchell (mitch@stride1.Stride.COM) Phone: (702) 322-6868 TWX: 910-395-6073 MicroSage Computer Systems Inc. a Division of Stride Micro. Opinions expressed are probably mine.