2.8M Floppy (Was: thinking of the "ultimate" retro x86 PCs -

Chuck Guzis cclist at sydex.com
Thu Jun 2 19:48:43 CDT 2016

On 06/02/2016 05:09 PM, Fred Cisin wrote:
> I hope that Chuck will correct some of the errors that I made below:

I think you've pretty much got it.

> No need for drivers IFF your hardware (FDC and BIOS) and OS were new 
> enough.  I think that SOME FDC boards that supported 2.8M data
> transfer rates had BIOS chip to "update" the system BIOS.

If the 2.88M-capable FDC wasn't part of the motherboard, it generally
had a BIOS on the card for the extra stuff.  This was certainly true of
the CompatiCard IV and a few other "special" FDCs (i.e., those with a
separate connector for a 2.88M drive).

NT 4 had no problem with the drives, but then, it could also support
3-mode drives (1.23M 360RPM 8x1024 format).  I believe that pin 4 on the
floppy interface was used to switch speeds.

> Was it 4.00 that added 2.8M?

Sounds right--but it may also be a matter of *which* 4.0.  MS or IBM?

> DRIVER.SYS V DRIVPARM=: DRIVER.SYS permitted using formats that were
> newer than the SETUP program knew about, such as 720K 3.5" on 5150
> and 5160, or pre 3.5" 5170. DRIVER.SYS created an additional drive
> letter, so the 3.5" drive would end up as drive D:
> DRIVPARM changed the specs of the drive without creating a new
> letter, so your 3.5" could still be B: DRIVPARM was undocumented in
> PC-DOS 3.20 and 3.30, but it WAS there, and worked just fine with
> generic BIOS. BUT, I was surprised to find it FAILING with real IBM
> BIOS (or image thereof) in the same machine!   Good reason to leave
> it out of the manual!

DRIVPARM was sort-of-disabled on PC-DOS 3.2 and 3.3.  You had to suffix
the "DRIVPARM" with three control-A characters (hex 01) to get it to
work.  At some point, the device types for SD and DD 8" drives were
nulled out, but I don't recall when.

> BTW, if you had four floppies installed, and the BIOS understood,
> then your floppies would be drives A:. B:, C:, and D:. and you hard
> drive would be drive E:.  But some programs were "hard-wired" to
> assume C: as the hard drive, including the INSTALL for MS-DOS 5.00!
> MICROS~1's answer: "Install it on drive C:, and then copy it to the
> hard drive that you want it on." I refused to install it to a 3"
> disk, so I installed on a different machine, and created a 360K boot
> disk, plus copied all of the other files to a sub-directory on the
> hard disk (E:).

At some point, MSDOS decided that the hard disk would always be C:, with
any additional removable drives trailing that.  That probably helped a
lot.  And there was always a drive B:, whether or not a physical drive
was present (if not, it mapped to drive A: with suitable prompting


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