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replacement for 80286

greg2002

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Ok, 2 questions....... I have an IBM AT 5170 Gen 1 (256/512 motherboard) with a 6MHz 80286. Can I just pop out the CPU and drop in a faster one ? Is so, what do you find to be the best CPU to replace it with ? The BIOS has been upgraded to the Gen 3 July 10, 1985 BIOS chips. Thanks !
 

maxtherabbit

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the short answer is 'no'

IBM did make a 8MHz AT, so you might be able to convert it but IIRC there is some kind of BIOS check that prevents over clocking
 

krebizfan

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There were kits with the higher clock oscillator and updated BIOS to go along with the new CPU. Note that the 10 MHz AT variant from IBM was a bit unreliable so pushing that far might be unwise. It wasn't 5170 but I think was the industrial system.
 

pinkdonut666

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I was in the same boat and wanted some more performance from one of my IBM AT's. Checkout my thread: HERE Where I'm going into my way of upgrading the machine. the First thing I thought of was an Intel Inboard AT, which was specifically designed to upgrade the AT to a 386. But they are very rare and expensive. Second option would have been something like a "make it 386" or Kingston "SLC NOW!" but these options again are very rare and expensive, and may have problems with the 5170 Bios or motherboard if they aren't specifically compatible.

My IBM 5170 in question was a 6mhz version 1 board that had an aftermarket AMI bios when i got it. So the fact that now it boots up with a phoenix bios message doesn't bother me too much. and I have to admit for about $100, it was an awesome bang for the buck upgrade.
 

pinkdonut666

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There were kits with the higher clock oscillator and updated BIOS to go along with the new CPU. Note that the 10 MHz AT variant from IBM was a bit unreliable so pushing that far might be unwise. It wasn't 5170 but I think was the industrial system.

I mean the PS/2 Model 30 286 in "sort of" an AT 10mhz... all be it with the stupid proprietary crap that comes with it being a PS/2.
 

greg2002

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This is not a machine I'm keeping, but to sell. I have 2 I'm keeping, an orignal Model 339 (Gen 3 8MHz) and a wolf in sheep's clothing, a 486 motherboard in an AT case, full ISA and lots of memory. I would think a simple upgrade to 8MHz wouldn't cause too much pain, but the performance gain might not be worth it. Thanks for you thoughts.
 

tipc

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The model 30/286 had a few 8 bit isa slots and no mc slots, no?

I had 1 for a while. It looked like a ps2 to me (or PoS v.2.0 :). I kind of liked the whole battleship bone color scheme. More cheery then the multinational corporate beige scheme. A twist of artsy fartsy. Even after my 30 got wet and spit sparks at me, it still worked. Built real well it seemed. But weird interleaved memory arrangement. Something screwy.
 

krebizfan

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The model 30/286 had a few 8 bit isa slots and no mc slots, no?

I had 1 for a while. It looked like a ps2 to me (or PoS v.2.0 :). I kind of liked the whole battleship bone color scheme. More cheery then the multinational corporate beige scheme. A twist of artsy fartsy. Even after my 30 got wet and spit sparks at me, it still worked. Built real well it seemed. But weird interleaved memory arrangement. Something screwy.

3 16 bit ISA slots and the world's slowest hard drive. Nice turbo AT clone except for the hard drive.
 

fatwizard

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I acquired a 1rst gen 5170 motherboard (512K stacked chips/6 MHz) that worked fine, but I didn't have a 5170 case to put it in. Later I got my hands on a whole 5170, but it's motherboard was damaged by battery leakage, and I could never quite get it working right. This system had the next gen motherboard with the 8 MHz CPU. The crystal is socketed on these boards so I pulled the 8 MHz CPU and crystal out of the damaged board and installed them on the 1rst gen board, then I built up the system around that. I've read that some of the support chips on the 1rst gen motherboard can sometimes be unreliable past 6MHz, but this one works flawlessly at 8MHz.
 

AndyM1981

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Has anybody ever tried to replace a 80286 with an 80386-SX?

Is that even a thing? Even though they both use a 16-bit bus I would assume that there are enough differences that you just can't pop in a 386SX and have it work. There are the likely differences in pin out, communications with the bus and BIOS support to name a few off the top of my head.
 

Eudimorphodon

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They sold 286-386sx upgrade boards that plugged into the CPU socket and basically had no glue on them so, yes, the 386sx is directly compatible from an electrical standpoint. (And while there are minor BIOS issues they can be worked around with drivers.) The main problem is Intel never released the SX in a physically compatible form factor; it *only* came in a surface mount flat pack, so you need an adapter board to put it in a 286 socket. To make it harder 286s actually came in several socket types, so you need a board that fits your particular motherboard.
 

maxtherabbit

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more to the point: why? clock for clock the 386sx is not faster than a 286, so unless you need to run 32bit code it's not gaining you anything
 

krebizfan

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Is that even a thing? Even though they both use a 16-bit bus I would assume that there are enough differences that you just can't pop in a 386SX and have it work. There are the likely differences in pin out, communications with the bus and BIOS support to name a few off the top of my head.

Not all that much difference. Some of the very early 386SX computers used 286 motherboards with a tiny daughtercard to hold the 386SX. Everex was one that did that in the rush to get a 386SX out the door.

Note that some of the upgrade boards included an oscillator allowing for a nice clock speed boost.
 
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Eudimorphodon

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more to the point: why? clock for clock the 386sx is not faster than a 286, so unless you need to run 32bit code it's not gaining you anything

The one reason I can think of for it is if you have a 286 with a lot of extended memory you’d like to be able to use as EMS, or to run multitaskers like Desqview.

Note of course that *most* 386sx upgrade boards sold commercially did have more than just the CPU on them because they often included some cache memory and a circuit to allow the CPU to run faster than the bus, but a very few “feature only” adapters that ran the CPU at the native speed did exist. It would be sort of amusing to have one of those in an original 6mhz AT.
 

Eudimorphodon

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It's kind of strange in retrospect that when clone CPUs from AMD and Cyrix became a thing that nobody released a 386sx variant in PGA and PLCC packages to directly plug into 286s. (From a strategic standpoint it makes sense that Intel didn't, because they really wanted to push new computer sales.) Cyrix in particular made internally clock-doubled 386sx clone CPUs that they could have packaged as plug-and-play boardless upgrades.
 
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