Remove the keyboard completely (that is, open it up as though you were going to use the computer, then press in the hings from the outside and take it off altogheter. Undo the 6 screws on the front of the machine (2 rows of 3, pretty obvious when you look at it). Put the machine screen-side down and lift the case up and off. Now put the machine down flat again. On most American units, there's a metal shield over the mainboard/expansion board slots. It's held on by 3 (IIRC) screws, at least one of which also holds an expansion board in place. Take these out, lift off the sheild. It's very tight!. It is a nromal XT mainboard, but slot 8 is unusable (there's very little space for it, and it needs a 'special' card anyway, like slot 8 on all IBM XT,s. The async card won't fit!). Slot 1 is taken up by the CGA card, slot 3 by the floppy controller. Slot 2 is a full-length slot, slots 4-7 are short slots, I think you can fit a serial or parallel card into those. The official way to add a hard disk is to put an expansion unit card into slot 2 (the only slot it will go in) and put the hard disk and controller in the expansion unit (5161). Rather spoils the point of having a 'portable'... You can put a half-helght hard drive in one of the floppy bays, get a controller card into whichever slot it will go in, and cable it up. My 5155 came like that (I bought it second-hand), I returned it to the 'stock' configuration of 2 floppies (even got a real IBM floppy drive...) One thing that is worth doing is the 640K mod. Being a normal XT motherboard, you can put 41256s in banks 0 and 1, 4164s in banks 2 and 3, a 74S158 (or 74F158) in the empty DIL socket at the front of the board, and solder a jumper between pads E1 and E2. Set the DIP swtiches for 256K (really, all 4 banks used), and you dnn't need any memory expansion cards... -tony