Xerox 820 system disks in Teledisk format?

On 5 May 2009 at 6:48, Dave Dunfield wrote: Well, I think Dave did A-D mostly for notational convenience. In fact, without any specific DOS mapping information, it might be more accurate to say "Port 3Fx, units 0-3", but that would really confuse the users. It's not the CompatiCard per se, (it's pretty neutral in terms of hardware), but adding controllers not on the primary port of 3Fx and DMA 2, IRQ 6. It's a little complicated as you may have to share IRQs and DMAs. FWIW, DOS does not provide a reliable way of figuring out what dirve letters are associated with what controller once you get above B:. Given the number of secondary FDCs out there (or lack of them) I don't blame Dave. Nor do I blame him for not including Backpack drive support. Speaking of adding floppy drives, one can sometimes find controllers that can be modified to handle more than 2 drives (several of ISA SCSI controllers, for example used the National DP8473 FDC (a great FDC, by the way that even formats and writes 128 byte MFM sectors, as well as FM), which allows for driving up to 4 drives--a little jumpering to the floppy header is often all that's required. Some older Pentium-era motherboard "Super I/O" chips can likewise be modified to handle more than two drives. So if you can't find a Compaticard, you're not out of luck. While programs such as ImageDIsk don't require software to access these extra drives, the motherboard BIOS doesn't usually support them. The SMSC ftp (ftp.smsc.com) has loadable DOS drivers for the extra units that provides BIOS support (and thereby DOS support) for the extra units. --Chuck