I/O port 0170H refers to the secondary *hard drive* address (the primary being 01f0H). The secondary FDC address is 037xH (the primary is 03FxH). Let me look around--I've got several old MS-DOS secondary port drivers kicking around here. A word of warning, however. For a secondary controller using the same DMA and IRQ (2 and 6) as the primary, the primary needs to have implemented the "enable" bit at I/O port 03F2H so it can float its own DMA and IRQ lines when the secondary controller is active. Not all controllers will do this, even though it's documented as part of the standard PC architecture. If you want to check out the operation of your secondary controller, hook a drive to it and find copy of FORMATQM or COPYQM (or 22DISK...) and set up a DISKETTE.CFG file for it to use. In the meantime, I'll look for a good driver. Cheers, Chuck -----REPLY----- Hi Chuck! Thanks to you and Mike S too for replying. I accidentally said $170 for the address but I really meant $3F0 and $370. I had been staring at these IO cards for a while and got confused. Sorry! The primary FDC am using ($3F0) is on a Western Digital ST-506/ST-412/FDC controller combo board. I have been using a variety of Multi IO boards trying to get the secondary FDC to work ($370). My plan is to share the DMA and IRQ lines which *should* work since I won't be using the drives at the same time. If you can find a driver which will let me access the drive from MS-DOS, that'd certainly be helpful. It is possible that the primary FDC is interfering with the enable bit but I will try the 22disk approach and see if that helps. I am kind of surprised this aspect of the project has been as much trouble as it has been. I would have thought the secondary FDC from DOS would have been well explored but there is practically nothing on the internet on the subject. This is easy in CP/M and seems like it would be in Linux too. I learn something everyday! Thanks for your help! Much appreciated! Andrew Lynch PS, I tried the 22disk approach and it worked like a charm. I think SDRIVE.SYS might be the problem. I was able to write a custom DISKETTE.CFG and format the disk in a CP/M format, copy files to it, and get a directory is basically good