IBM PC/XT Clone "Blue Chip"... I take it you do not have any of the original parts to replace due to non-operation so hoping your machine is similar to mine, here are my specs: the controller card is a Wester Digital MFM 8-bit ISA controller card # WDC 60-000156-02 REV XO connected to a Seagate ST-225 21mb HDD. I do know that the ST11R controller card with ST225R HDD won't work on my rig even though everything shows up when booting because the bios revision for this setup is different than that of my computer, it will not let me format the disk because the "software is incompatible or bad track1 sector", so even though it sees it, it won't let me load software. Since I have a WD MFM card, I will try to locate another ST-225 MFM HDD. I also do know that Seagate made controller cards ST01/02, ST10, ST11, all I've found so far and they go to different size hdds. To find parts, eBay is the place to go, besides the recyclers, but expect to spend a few bucks, these parts aren't cheap for this computer. Please keep in mind you must have it as a "set" to insure it wil work properly. You cannot intermix controller card with these hard drives, they simply will not operate. Hope this helps you out cause I'm doing the same thing for backup parts before they don't exist anymore.