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How to configure modern PC to take 80 track QD drive

carlsson

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People sometimes report the ability to get a standard PC to take a 80 track floppy drive of the DD/QD variety, the ones that in native FAT12 format would hold 720K.

I have a couple of suitable drives but so far have failed to get them to work as 80 track drives. Most specifically I have a Mitsubishi MF503A-301ME which comes from a BBC Micro floppy drive (User Friendly Drive). It has a toggle switch on the front to select between 40 or 80 track mode.

My modern PC is an ASUS A7S333 with an AthlonXP 2000+. The board has a decent FDC, at least good enough to read and write foreign MFM formats with a 40 track drive. There may be more capable motherboards, but there certainly are less capable ones too.

Anyway, when I connect the Mitsubishi drive in 40 track mode to the PC, I can configure BIOS as a 360K drive, either A: or B: depending on which cable end I use. The drive is jumpered as DS1. In this mode, it works like just about any 360K PC drive when it comes to reading and I suppose writing floppy disks.

When I toggle it to 80 track mode, the problems occur. Since BIOS obviously doesn't have a suitable setting, I tried to fool it to accept the drive as a 5.25" 360K drive (BIOS error) or a 3.5" 720K drive (also BIOS error). In this case, I can press F1 to bypass the errors but it also appears to make the drives inaccessible as a whole.

I tried to set BIOS to 5.25" 1.2MB which is accepted by the computer (probably due to both QD and HD are 80 track drives) but whenever I try to access the drive from DOS, it reports errors.

So which way should I go ahead? Is the above behavior typical? Should I try to dig out another PC? I have various kinds from 386 to Athlon to try in case some BIOSes and chipsets are more forgiving and will try to address "unknown" formats until they physically fail.

Or should I rather look for a 1.2 MB drive which has been reported to at least read and in good cases write 80 track QD floppy disks? For reference, I have no false hopes of working with the 100 tpi PET/CBM formats, just some more traditional 640K MFM formats like the above mentioned BBC Micro, Philips P2000c (CP/M) and perhaps others.
 

Chuck(G)

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A PC with a floppy interface isn't "modern" by any stretch. "Modern" PCs have no legacy floppy capability. Having said that...

A 1.2MB should have no problem writing QD floppies. Just be aware that most 1.2MB drives use a data clock of 300KHz, not 250 and all BIOSes that I know of double-step in low-density mode. Still, with a suitable driver, that shouldn't be a problem.

Your comment about a Mitsubishi drive in "40 track mode" has me a little puzzled, however. What on earth are you declaring it as to the BIOS to get it to double-step?

There should be no problem declaring a 5.25" QD drive as 720K 3.5". There's really no difference electrically, save for some features such as Disk Changed (if your drive delivers a READY signal, you should isolate that pin (34) and try it again)

I've been running 96 tpi QD drives (mostly Teac FD55Fs) on PCs since my first 5150 in 1983.
 

carlsson

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Ok. I just figured 1.7 GHz systems running Windows XP were off-topic for this forum, but if we draw the line to those systems which have legacy floppy support, it seems several Athlon64 (socket AM2+) systems are vintage by the day they leave the factory... ;-)

My Mitsubishi floppy drive has a switch that will set it to 40 or 80 tracks. I don't know how the drive internally handles that, if it will move the head in steps of two tracks whenever used in 40 track mode.

I will try with some other PC old enough to have a floppy drive interface (actually all my desktop PC's except for my Asus Barebone Pundit does) and new enough to easily retrieve files to and from it.
 
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