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20 MHz 286 with 4 MB of RAM

Mike Chambers

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Sep 2, 2006
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i'm not the one selling it. i found it on ebay, it's a buy-it-now listing. the CPU is made by Harris. this thing looks pretty crazy for a 286. the price is $100, and i can't justify spending that much on it but i figured somebody here could. :p

the most interesting thing to me is that the memory isn't put directly on the board, it has 4 SIPP sockets.

Picture%20122.jpg


http://cgi.ebay.com/Fast-20MHz-286-...emQQptZLH_DefaultDomain_0?hash=item414e93a5c6
 

vwestlife

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This looks pretty early for a 20 MHz 286 board, since it has both DRAM sockets and the fairly uncommon SIPP sockets.

Later 286-20 boards were barely longer than the ISA slots, used highly integrated circuitry (very few chips on the board), and had 4 SIMM sockets.

A 286 at this speed can easily keep up with a low-end 386 when running DOS applications.
 

Mike Chambers

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actually, i might be wrong but the empty sockets lining the right hand side look like they're for cache to me.
 

vwestlife

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actually, i might be wrong but the empty sockets lining the right hand side look like they're for cache to me.

The seller wrote that it has "sockets for 1 MB of DIP type RAM and four 30-pin SIPPs(comes with 4 MB of SIPP RAM installed)." I don't know of any 286 with onboard cache.
 

Mike Chambers

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heck yeah, put it up on the eGay. especially if you have more than one. anyway, whichever one of you bought it is obligated to set up a web server on that mobo so we can all see how it runs it.
 

pianoman72

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I bought the motherboard. Thanks for pointing to the link on Ebay, Mike, I just couldn't resist getting a really fast 286 setup, after having wanted one for a long time. Now, which coprocessor would you guys recommend for this motherboard? I only have a 80287-8, so I doubt that would work at 2/3 the speed of this 20mhz CPU.

About the web server, I'm afraid I do not have any ISA network cards with which to set it up. Even if I did, I wouldn't know how to set that up in DOS, as I've never done it before. However, I would be willing to learn, if I could get a hold of the needed hardware.

I'm excited about installing the motherboard in my setup.
 

vwestlife

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20 MHz 80287 coprocessors do exist, but are rare. Intel had their 80287XL, which was internally a 387SX scaled down fit a 287 socket and with an internal 3/2 clock multiplier so that it would run at full CPU speed instead of 2/3rd the main CPU speed, but I don't know if Intel ever put out a 287XL rated for 20 MHz.
 

MikeS

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heck yeah, put it up on the eGay. especially if you have more than one. anyway, whichever one of you bought it is obligated to set up a web server on that mobo so we can all see how it runs it.
Darn! I know I had one but can't find it; musta sold it already and forgot. So you can relax, pianoman, I'm not going to sell one for $10.00 and make you feel bad; besides, mine only had 1MB.

I do have some 16MHz boards though... and they use easier-to-find SIMMs... anybody tempted?
 

pianoman72

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Hmm, since it's very difficult to find a 20mhz 287 chip, would you recommend that I try plugging in my 80287-8 chip to see what happens? Would that damage the coprocessor or any other component on the motherboard? Or maybe I should not take a chance, and just leave it without the coprocessor, unless I can find one at the rated speed someday.

Also, what kind of external battery should I look for? I would need one to keep the BIOS settings + time, since the internal one has been removed.
Thanks for all the help, everyone.
 

vwestlife

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You mean "late", don't you? I've got a 386 board set up that way (SIPPs and DIPs). An early 286 wouldn't have the C&T chipset, but discrete TTL.

I dunno... I just remember the 286-20 boards that used a handful of large VLSI chips (like a PS/2) and were very short, not much longer than the ends of the ISA slots. Mail-order companies like JDR and Dalco sold these boards well into the mid 1990s.

Picture something like this, just with a 286 on it instead:
15yxcgn.jpg
 

pianoman72

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Interesting, after searching the web, I found that there is only one 287 coprocessor rated at 20mhz, named IIT 2c87-20.
Good news, as my earlier searches did not bring such result, naturally since I only looked for Intel 80287 chips, which go only up to 12mhz.
Now if I could only find a good deal, I would consider getting one.
 

Chuck(G)

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I dunno... I just remember the 286-20 boards that used a handful of large VLSI chips (like a PS/2) and were very short, not much longer than the ends of the ISA slots. Mail-order companies like JDR and Dalco sold these boards well into the mid 1990s.

The OP's board looks to be XT sized; i.e., "Baby AT". But the 386 SIMM/SIPP board I have is a big one also--and it has the "staggered" 64K/1M DRAM sockets in addition to 4 SIPP sockets. There was quite a bit of overlap in dates of manufacture of 286 and 386 boards. My Micro 386-16 is full-sized PC AT and has no memory on the planar--it all fits into a special expansion card. A blazing 16 MHz.

BTW, does anyone have an 8 MHz 80287 available? The socket is for a 287, not a 387 on mine (40 pin DIP). I wonder if it would help Win95 to run faster.
 

Anonymous Coward

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Cyrix also made an 80287 FPU that would run at 20MHz. Cyrix Fasmath 82S87. Those are pretty rare though. You might be able to get the intel 80287XL to 20MHz though. Intel only rated it for 12.5 MHz because that was the fastest 286 chip they produced, but since 80287XL is based on the 80387SX core, it can likely do 16 or 20MHz. I would use a heatsink to be safe though. Keep in mind that i287XL, Fasmath 82s87 and IIT 2C87 all use the 3/2 multiplier because the original AT boards used a 2/3 divider. So if you try to run a 20MHz FPU on a board without the 2/3 divider, you'll end up overclocking to 30MHz.
 

pianoman72

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Denton, Texas
Would I be able to tell if the motherboard has a 2/3 divider, by looking at the 2nd crystal (besides the main 40mhz CPU one) on the board?
Would my 8mhz 287 function at all if overclocked around 13mhz (given that the board has the 2/3 divider)?
Thanks for all the help.
 

Anonymous Coward

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From looking at the photo, it appears that the FPU oscillator has not been soldered in. I would guess that if you soldered in a socket and a jumper, you could have the FPU run at any speed you want. Though I've never seen a 286 board with a separate oscillator for the 287 like that before.
 
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