Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!uunet!bu.edu!polygen!jerry From: jerry@polygen.uucp (Jerry Shekhel) Newsgroups: comp.sys.amiga.advocacy Subject: Re: The 68050 - end of the 680x0? (was Re: The Amiga's Future) Message-ID: <1147@stewart.UUCP> Date: 20 Jun 91 18:26:16 GMT References: <5068@orbit.cts.com> <16647@darkstar.ucsc.edu> < <1308@cbmger.UUCP> <28@ryptyde.UUCP> > <01dH!cmr@cs.psu.edu> <1991Jun10.072945.8821@neon.Stanford.EDU> <22365@cbmvax.commodore.com> <1135@stewart.UUCP> Reply-To: jerry@stewart.UUCP (Jerry Shekhel) Organization: Polygen Corporation, Waltham, MA Lines: 76 daveh@cbmvax.commodore.com (Dave Haynie) writes: > >The unified cache is an obvious example >of this -- Intel's even using split caches themselves in their other chips, >because they simply result in better performance. > Are you suggesting that the unified cache is a limitation designed to ensure MS-DOS compatibility? How would a split cache break MS-DOS? > >Sorry Jerry, it isn't. The fact that the i860's data cache operates only in >copy-back mode, and provides no snooping mechanisms, make it ill suited for >use as a coprocessor, since all cache consistency must be handled in software >alone, that's a significant performance hit. Both of these problems are >apparently cured in the new chip. > And yet the i860 is used all over the place as a coprocessor, but only in a couple of places as a CPU! I don't know enough about it, but it makes me wonder. > >Yet, the 486SX, at least presently, costs the same to make as the 486, since >it's the same die. They're selling, as always, based on their captive market. > I agree. Actually, I'd bet that the 486SX costs less to produce, since the yield is probably much greater. I wouldn't be surprised if a large part of 486SX production consisted of reject 486 chips that failed the speed test or ended up with defective FPUs. > >The '486, in its native mode, isn't really that great a 32 bit processor, but >it isn't bad. The architectural baggage it carries around necessary to support >MS-DOS and 8086 emulation modes is what makes it ugly. The unified cache >without copyback, the simplified MMU, various other architectural details make >the '486 inferior to any other 32 bit processor of this generation. Which is >why so many '486s are sold into PC Clones, those that go elsewhere are virtlly >insignificant. A few very companies pick the '486 for use outside the PC Clone >market (other than Intel), and that's usually because they're running software >developed on the PC. > While I agree that the 486 instruction set is a bit dated, I wonder what you mean by "simplified MMU". It does the job. How is it "simplified" or "limited"? Also, there are several companies which produce multiprocessor 486 systems that have nothing to do with DOS. As for me, I got a 386 because it's a cheap UNIX platform that's plenty fast enough for me. Once you have UNIX, who cares what the processor is? I used an SGI for years before finding out what kind of CPU it had. > >Sure seems to me that you're the one not supplying any information. If I >say "it is", you can sure say "it isn't". But when you ask me to supply fact >to back my points without supplying any yourself, you're the one who's going >to come out looking foolish. > I don't think so, Dave. You said, "It sucks because it's braindead." I said, "Prove it." How was my reply foolish? Maybe your original statement was the more foolish one? >Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" -- +-------------------+----------------------+---------------------------------+ | JERRY J. SHEKHEL | POLYGEN CORPORATION | When I was young, I had to walk | | Drummers do it... | Waltham, MA USA | to school and back every day -- | | ... In rhythm! | (617) 890-2175 | 20 miles, uphill both ways. | +-------------------+----------------------+---------------------------------+ | ...! [ princeton mit-eddie bu sunne ] !polygen!jerry | | jerry@polygen.com | +----------------------------------------------------------------------------+