Xref: utzoo comp.unix.sysv386:742 comp.os.minix:12524 Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!isis!ico!rcd From: rcd@ico.isc.com (Dick Dunn) Newsgroups: comp.unix.sysv386,comp.os.minix Subject: Re: 286 -> 386sx Upgrades Summary: observations on these upgrades; some tradeoffs Message-ID: <1990Sep25.224438.6687@ico.isc.com> Date: 25 Sep 90 22:44:38 GMT References: <40019@cci632.UUCP> <1990Sep21.144108.1098@pmafire.UUCP> <1990Sep25.152828.7408@pmafire.UUCP> Organization: Interactive Systems Corporation, Boulder, CO Lines: 64 tuv@pmafire.UUCP (Mark Tovey) writes about upgrading a 286 AT to 386: [> > is also Tovey] > > I have a friend who has found a 386sx upgrade kit. Apparently you > >remove the 286 chip and install a plug in daughter board in place. > >This board contains the 386 chip, a socket for a coprocessor (you can > >continue to use the 287 if desired) and any necessary support > >circuitry. I tried a couple different flavors of these and returned both. I've looked into others and rejected them all for one reason or another. One thing you've got to watch out for is whether the add-in board will fit the space available. One board would almost fit, except for obstruction by a power- supply connector which came up too high. I tried to raise the daughter- board with a chip carrier; this introduced a noise problem and it wouldn't work. Look at the size and layout of the board, then look at where your 286 sits (paying attention to location of pin 1). You'll need to get the info for the right kind of CPU package (PLCC or PGA). Looking at the SOTA ad, I noticed that they seem to have arranged their PGA board so it won't clear a ZIF socket right! (A ZIF has a lever along one side to apply the pressure to the contacts. This requires that a daughterboard mount the pins to the old processor socket along an edge of the board.) Most clones use PLCC instead of PGA; make sure the vendor of the board offers the right connection. Also, if you're looking at this for a UNIX machine, be *sure* you can return it if it doesn't work for you--and try it out with UNIX right away. Often, add-in boards have only been tried with DOS, and a support call will only get you a "What's a UNIX?" Also, there's the problem of boards which aren't really hardware-compatible; they're "BIOS-level" compatible--no use for UNIX, which doesn't use the BIOS. > I managed to track my friend's source. He got the information from > the August 20 issue of InfoWorld, page 83. The company that > manufactures it is: > SOTA Technology Inc. [details deleted] > It uses a 16MHz chip and comes with 16k of cache memory... >...The cost is a little steep, it lists for $595.00. This may or may not > be cheaper than replacing the motherboard and memory, depending on > your configuration... $595 is definitely steep. You should be able to get a complete SX mother- board for $400 or less; that will leave you $200--with which you can go out and buy 4 Mb of memory. (Well, 1Mx9 80ns SIMMs are almost down to $50; they probably will be by the time this message gets out.:-) Thoughts on relative advantages: The daughterboard has a cache. This will help performance in some areas, *assuming* the cache works right (e.g., doesn't tangle with I/O ports, memory-mapped I/O devices, or DMA). It will let you use existing (bus) memory, which would be good if you've already got a lot. BUT if you've gotten a lot of bus memory, that might have come about because you needed it (:-) for large programs and/or lots of data--in which case the cache is likely to be inadequate. If you're upgrading an old machine, consider that bus speed is probably 8 MHz tops; that's a 125 ns cycle. An access to bus memory takes 3 cycles, or 375 ns. per 16 bits. By comparison, if you replaced the entire motherboard, you'd put normal 80-ns memory on it. Some trickery actually allows the 16-MHz SX motherboards (that's 62.5 ns cycle) to use 80 ns memory without a wait state on every access. Anyway, ignore the details; you should be getting the idea: old slow bus memory plus a cache may lose against faster on- board memory. And if you don't already have a lot of bus memory, memory expansion is cheaper with the new motherboard. -- Dick Dunn rcd@ico.isc.com -or- ico!rcd Boulder, CO (303)449-2870 ...Worst-case analysis must never begin with "No one would ever want..."