There's 2 ways, the expensive easy way, and the expensive time consuming pain in the ass way.

The expensive easy way is finding an upgrade socket accelerator, which may be 386SX rather than 286 and those tend to run $400 or so on eBay.

The expensive hard way is replacing all the RAM chips with faster ones, some of the logic and he crystals in the timing circuits, plus the CPU, this can possibly run to about the same depending on what deals you can find.

The way to not quite do it, is try overclocking current CPU or replacement to 10 Mhz and seeing if things cope. Fairly good chance if you've got AC, if you're trying to do this in 30C ambients you might not get anywhere.

BitWrangler wrote on 2025-07-07, 00:11:

There's 2 ways, the expensive easy way, and the expensive time consuming pain in the ass way. […]
Show full quote

There's 2 ways, the expensive easy way, and the expensive time consuming pain in the ass way.

The expensive easy way is finding an upgrade socket accelerator, which may be 386SX rather than 286 and those tend to run $400 or so on eBay.

The expensive hard way is replacing all the RAM chips with faster ones, some of the logic and he crystals in the timing circuits, plus the CPU, this can possibly run to about the same depending on what deals you can find.

The way to not quite do it, is try overclocking current CPU or replacement to 10 Mhz and seeing if things cope. Fairly good chance if you've got AC, if you're trying to do this in 30C ambients you might not get anywhere.

Thank you for your reply, but to hell with all that. This computer is very sentimental to me as I have had it my entire life. So I don't want to risk destroying it by attempting an upgrade that is far too over my head.

Just out of curiosity, I have an old ibm clone with a faulty power supply. The clone has a 10mhz 286. Would I be able to swap the cpu in the 5170 with that 10MHz 286 without doing all the things you mentioned in your reply?

Pizmo wrote on 2025-07-07, 01:55:

BitWrangler wrote on 2025-07-07, 00:11:

There's 2 ways, the expensive easy way, and the expensive time consuming pain in the ass way. […]
Show full quote

There's 2 ways, the expensive easy way, and the expensive time consuming pain in the ass way.

The expensive easy way is finding an upgrade socket accelerator, which may be 386SX rather than 286 and those tend to run $400 or so on eBay.

The expensive hard way is replacing all the RAM chips with faster ones, some of the logic and he crystals in the timing circuits, plus the CPU, this can possibly run to about the same depending on what deals you can find.

The way to not quite do it, is try overclocking current CPU or replacement to 10 Mhz and seeing if things cope. Fairly good chance if you've got AC, if you're trying to do this in 30C ambients you might not get anywhere.

Thank you for your reply, but to hell with all that. This computer is very sentimental to me as I have had it my entire life. So I don't want to risk destroying it by attempting an upgrade that is far too over my head.

Just out of curiosity, I have an old ibm clone with a faulty power supply. The clone has a 10mhz 286. Would I be able to swap the cpu in the 5170 with that 10MHz 286 without doing all the things you mentioned in your reply?

Yes if it’s pga but it will only run the same speed your existing CPU runs.

There were some rare dinguses that fit an AT that allowed you to choose any frequency you wanted but your board still can only run as fast as components and bios allow, which may only be 8.5mhz.

Worth noting LATE IBM 5170’s ( aka 1987ish) would generally overclock to 10mhz but you would still need
1. Compatible generic AT bios
2. New clock crystal
~3. Potentially a 10mhz CPU

https://forum.vcfed.org/index.php?threads/ibm … -upgrade.68451/

Beware, some older 5170 BIOS versions are said to have a speed check against overclocking.
They're limited to 6 - 8 MHz operation.

But it not difficult to use an replacement BIOS.
There are at least 3 other BIOSes. Award, AMI, Quadtel etc.

I'm not sure anyone ever made a PGA 16 MHz 286, and the 5170 probably won't run stable at that speed anyway.

Your best bet is probably to find a 12 MHz PGA Intel 286 (which they did make, though they are hard to find - 10 MHz PGA is easier to find).

Yes, you'll need a third party BIOS.

And you'll have to replace the crystal. Luckily it's socketed.

And you'll probably have to look at those RAM chips, which might choke on you even at 10 MHz.

So you need all this:

-New 10 or 12 MHz CPU
-Third party BIOS
-20 or 24 MHz crystal
-Faster RAM chips (120ns or better to start with)

Assuming your AT hasn’t already been overclocked, then it’s safe to assume you have the type III motherboard (model 339) as that was what shipped with the 8 MHz system. Only the 6mhz type 1 motherboard could be freely overclocked, so any tinkering will indeed require a BIOS replacement. I believe someone on vcfed released an original patched BIOS many years ago that removes the speed governor.

16mhz and 20mhz PGA 80286s do exist. They were made by Harris, but weren’t common… therefore not cheap. But this isn't much of an issue as the 5170 board will never reach those speeds without clock doubling. In theory it should be possible to design a clock doubling circuit, but without cache you’d hardly notice the difference. Designing an upgrade with cache would really increase the complexity, and you’d be better off just shelling out the $$$ and buying a ready made upgrade (usually based on 486slc.

I recommend just doing a board swap. It’s probably the cheapest and easiest way.

I started pondering if one could use it as a backplane with one of the "crappy" ISA 386SX16 backplane mother-cards that used to be common and cheap, but even stuff like that is $500+ on fleabay these days... idea would be to break out some chip enable pins and be able to switch back and forth between onboard system and backplane system, sharing storage/expansion ... with unit off.

Now you're getting into "just buy an Intel Inboard" territory.

At some point you have to say this: a 5170 is a 286 machine. In fact, it is *the* reference 286 machine for IBM-compatibles. That's the spirit of it. It makes sense to try to push it to its limits, but too many system-replacing upgrades and you just have a different computer in your 5170 case, and it's not even a 5170 any more.

There’s no point to use an SBC unless it’s cheaper than a new motherboard.

There are really only few things that make the 5170 unique compared to a generic 286. Most being irritants. The speed governor. Weird double stacked memory chips If you’re using a type 1 motherboard. Built in BASIC…and some annoying BIOS routine that locks you into the stock hard disk controller. Oh, and the colour burst adjustment for CGA composite mode. You could probably replicate most of these behaviours by stuffing the IBM BIOS onto a generic 286 motherboard.

Personally, I'd leave it as close to "factory original" as possible... The IBM AT was a big step in PC evolution, and (at least to me **) is more interesting from a historical perspective than as a usable machine today.

The AT is a 286 ... If you spend some time looking, there are MANY much faster used/cheaper systems that can be had (in some cases for almost nothing)

Heck, I'm sure you can emulate it faster on modern hardware... (if you really need AT/286 hardware)

**Have a look at "Daves Old COmputers" - I've been interested in historically accurate machines for quite a while!

I believe swapping to a non-IBM BIOS provides a slight speed-up on its own. (something to do with RAM refresh or DMA channel 0, I think.) I noticed a 5~6% difference in SNOOPER when I put an AMI BIOS in my AT.

I tried overclocking to 10MHz as well, and the system booted but only with 512KB of RAM. The old memory expansion card was too slow for 10MHz.

BTW, as unlikely as it may seem, plugging a PLCC 286 into a through-hole PLCC socket and plugging that into the PGA socket also works as an option for swapping to a faster CPU. (Though the fitment of the two sockets is not terribly secure. I wouldn't try it in a tower case.)