4 floppy disk drives on a PC?

If 'PC' means an IBM5150, then yes, trivially. A: and B: connect to the intenral drive cable, C: and D: connect to the DC37 socket on the back of the card. But I guess that's not what you mean (this card supports 360K and 720K drives only, BTW). The intrrupt is not the problem (you can share interrups on the iSA bus provided you don't want them both enabled at the same time, which you wouldn't here). Most controllers, alas, do not support alternative addresses, but one time, in a fit of madness, I did a cut-and-jumper mod to add an inverter to one of the address lines going to a UMC disk controller chip to get it to a different address (this was to put _6_ drives on my PC/XT, the last 2 being 8" on this hacked controller). MS-DOS, and pesumably Windows, will not support 2 disk controllers automatically , or even easily. I believe linux does, it'll even support up to 4 drives per controller (if you look at how the drive select bits are allocated to the output port, it's obvious how this would be extended for 4 drives). I wrote my on MS-DOS software to handle the 8" drives (I wanted them to read/write PERQ interchange disks, so only being able to use them from that special program was not a problem). -tony