secondary FDC on PC with MS-DOS?

M H Stein dm561 at
Tue Feb 19 10:17:54 CST 2008

-------------Original Message:

Date: Mon, 18 Feb 2008 18:47:10 -0500
From: "Andrew Lynch" <lynchaj at>
Subject: secondary FDC on PC with MS-DOS?


I am building a test station using an old 486 ISA only computer to test
floppy disk drives and old ST-506/ST-412 style hard disk drives.

The computer seems to work OK and has a Western Digital ST-506 MFM hard disk
controller with a FDC on the card (IO address $1F0).

To help with testing floppy drives, I thought I would add a secondary FDC
however that is turning out to be much more difficult than I planned.

It seems there are drivers required to make floppy drives attached to the
secondary controller appear as drive letters under MS-DOS.

I searched around a bit and found SDRIVE.SYS which refuses to acknowledge
any of the other FDCs I place in the computer at the secondary address (IO
address $170).

There are some references to a DC2.SYS program but I cannot find it anywhere

Does anyone know how to add multiple FDCs to a PC so I can have multiple
floppy disk drives?

Of course, the Compaticard IV would be nice but those are very expensive and
almost unobtainable these days.  I have a Compaticard I which "sort of"
works but the drive gives errors every other time I access it.

Thanks in advance for any help -- especially if someone could send me or
tell me where I could find the DC2.SYS files.

Andrew Lynch

You could also look for a 4-drive FDC with its own BIOS; I'll dig through the pile 
& see if I've got one to spare.

Meanwhile, try asking on the Vintage Computer forums; there were some 
mentioned there recently.


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