jcallen@Encore.COM (Jerry Callen) (01/22/91)
In article <PCG.91Jan20191955@teacho.cs.aber.ac.uk> pcg@cs.aber.ac.uk (Piercarlo Grandi) writes: >The 68451 was not that long coming, and could be used as a TLB. Yes, it >was slow. Hmmm, what _is_ this part? I see from my Arrow catalog that I can order one, and it's described as an MMU, but my M68000 Family Reference never mentions it. Is it an early version of the 68851? -- Jerry Callen jcallen@encore.com
skipper@motaus.sps.mot.com (Skipper Smith) (01/23/91)
In article <13875@encore.Encore.COM> jcallen@encore.Com (Jerry Callen) writes: >In article <PCG.91Jan20191955@teacho.cs.aber.ac.uk> pcg@cs.aber.ac.uk (Piercarlo Grandi) writes: >>The 68451 was not that long coming, and could be used as a TLB. Yes, it >>was slow. > >Hmmm, what _is_ this part? I see from my Arrow catalog that I can order one, >and it's described as an MMU, but my M68000 Family Reference never mentions it. >Is it an early version of the 68851? > >-- Jerry Callen > jcallen@encore.com The 68451 was an MMU designed to be used with the 68010. It was a segmented MMU, real slow, and has generally been surpassed in every category (performance, speed, capability, etc...) by the 68851 and the MMU built into the 68030. I highly doubt that Arrow actually has any parts in stock (since it is a part which Motorola doesn't recommend for new designs), but they might just have a couple of them lying around somewhere. Another place to check would be with Krueger Electronics (a used part house somewhere in New Jersey, I think). -- Skipper Smith | skipper@motaus.sps.mot.com Motorola Technical Training | 8945 Guilford Rd Ste 145 All opinions are my own, not my employers | Columbia, MD 21046
davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr) (01/24/91)
In article <1991Jan23.154244.8322@motaus.sps.mot.com> skipper@motaus.sps.mot.com (Skipper Smith) writes: | The 68451 was an MMU designed to be used with the 68010. It was a segmented | MMU, real slow, and has generally been surpassed in every category (performance, | speed, capability, etc...) by the 68851 and the MMU built into the 68030. I Was this the one used in the unix-pc/7300/3b1/safari box? Both of mine have gone to new homes and I can't check easily. -- bill davidsen (davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen) "I'll come home in one of two ways, the big parade or in a body bag. I prefer the former but I'll take the latter" -Sgt Marco Rodrigez
croft@csusac.csus.edu (Steve Croft) (01/26/91)
In article <3149@crdos1.crd.ge.COM> davidsen@crdos1.crd.ge.com (bill davidsen) writes: >In article <1991Jan23.154244.8322@motaus.sps.mot.com> skipper@motaus.sps.mot.com (Skipper Smith) writes: > >| The 68451 was an MMU designed to be used with the 68010. It was a segmented >| MMU, real slow, and has generally been surpassed in every category (performance, >| speed, capability, etc...) by the 68851 and the MMU built into the 68030. I > > Was this the one used in the unix-pc/7300/3b1/safari box? Both of mine >have gone to new homes and I can't check easily. The 7300 has a MMU built from programmed logic chips... steve
mike@thor (Mike Haertel) (01/27/91)
In article <3149@crdos1.crd.ge.COM> davidsen@crdos1.crd.ge.com (bill davidsen) writes: >In article <1991Jan23.154244.8322@motaus.sps.mot.com> skipper@motaus.sps.mot.com (Skipper Smith) writes: >| The 68451 was an MMU designed to be used with the 68010. It was a segmented > Was this the one used in the unix-pc/7300/3b1/safari box? Both of mine >have gone to new homes and I can't check easily. No, the 7300/3b1 uses an array of 1K words of fast static ram to hold the page table for 4 megabytes of memory. (4K pages) in order switch context you have to copy the new page table in and clobber any parts of the old that you didn't overwrite. this is rather like the early Sun MMU i guess, except that you don't have multiple contexts. -- Mike Haertel <mike@stolaf.edu> "He's a tie with the ambition to become a full-blown suit." -- Jon Westbrock