What kind of ram do i need if i dont have ram in another motherboard

My HP motherboard died, so i replace it with a used IBM motherboard, but i didn't have ram in it, so how do i know what ram to place n it

What may not be so easy is using the same OS.

Don't know whether your two mobos use different chipsets, which could cause difficulties should you try to boot up your old HD. Using a "Recovery Disk" has the same result, and may not work anyhow now that the BIOS is no longer HP.