The crystal is in the motherboard. Take a picture of the motherboard.

jesolo wrote:

The crystal is in the motherboard. Take a picture of the motherboard.

Basically I am considering if I should buy ibm ps/2 model 25 with 8086 8Mhz and I am wondering if I could make it compatible with those games that are speed sensitive and require 4.77Mhz pc to run at correct speed. I don't have picture of the motherboard at the moment. I know the cpu can be replaced with NEC V30 without changing crystal to make it faster, but I wonder if same thing works with making it slower.

Somebody will correct me if I'm wrong but I'm quite sure the 8284 clock generator divides the crystal rate by 3. Given that, the 8mhz 8086 would have a 24mhz crystal.

14.318180MHz crystal works out to 4.77mhz cpu. The isa bus and keyboard rely on this crystal as well.

Another option is to buy a 286 and use software to slow it down, thats also worth some research.

An 8086 at 4.77 MHz is still much faster than an 8088 at 4.77 MHz, so it is not likely to solve all your speed-sensitivity problems.
A clone with a real 8088 and a turbo option is a better solution to that.

Scali wrote:

An 8086 at 4.77 MHz is still much faster than an 8088 at 4.77 MHz, so it is not likely to solve all your speed-sensitivity problems.
A clone with a real 8088 and a turbo option is a better solution to that.

Too bad. This is the slowest pc I have seen for sale during past 2 years.

Baoran wrote:

Too bad. This is the slowest pc I have seen for sale during past 2 years.

I don*'t know for sure, but perhaps it's possible to change memory-refresh timings via software to make performance worse ?
I remember that people decreased the refresh times to make a machine faster, maybe it also works in reverse (longer refresh cycles) ?
This is just an idea; and not a very good one. But it's the only thing that comes to mind now.
That being said, I'm no XT machine expert. Still learning..