<Guys, everyone should have this book by Scott Mueller, "Upgrading and <Repairing PCs". Tis' have good INFO on most PS/2, PS/1 and some late <IBM boxens including the PC, XT and AT in all types, convertible, <5155 portable. I have that book and it's leaving me guessing on some of this. <Not in this sense. Correctly stated, in IBM's words: for this 50 <series uses either MFM/RLL card that plugs into that MCA bus or the <IDE MCA hd and pass thru card called IDE (MCA IDE) on Interposer <Card. It must be the mfm/rll as the card in the MCA bus is fairly busy and the drive is sparse. <BTW, got a spare working 1.44 FDD for that 50 series? All I have is <this battle damaged naked 50Z board with CPU and rom with stand up <floppy adaper. Or better yet, any luck finding a spare PS/2 with <386 or better boxen? I have no desire to get into MCA bus or for that fact PS/2 or machines of that era. Older ISA I have but that's it other than the more current 386 and 486 box to run mail, linux and gcadd. I may trade off these ps/2s. Allison