720K on PC (was: DD disks and HD drives (was: Where can I find...)

From: Fred Cisin <cisin_at_xenosoft.com>
Date: Mon Jun 26 15:58:30 2000

> [ 5.25" 80 cylinder 96 tpi drives on IBM PCs]
> > without special software. (Unless we happened to have one of the few MS-DOS
> > machines that supported the format like Tandy, Victor, and Epson if you wanted
> > to pay the exhorbitant price they charged for a compatible 96 tpi drive.)
> Why couldn't you simply set it up as a 720K (3.5") drive on _any_ PC?

PC-DOS and MS-DOS from version 3.20 on fully support 720K; It doesn't
matter whether it is 5.25 or 3.5; the computer can't tell them apart.

If you are putting the 5.25" 720K drive in an AT, set the CMOS for
3.5" 720K.

On many/most you will need to add a line to CONFIG.SYS of either
DRIVER.SYS (which creates an additional drive letter), or DRIVPARM (which
changes parameters for existing drive). ("/D:1 /F:2" to use drive B: as

DRIVPARM is documented in MS-DOS. It is present, but not documented in
PC-DOS (3.20 and above).

Here's a puzzle for you:
DRIVPARM in either PC-DOS or MS-DOS 3.20 will work on most compatibles.
But on real IBM machines, DRIVPARM fails and gives an 'unrecognized..." in
the processing of CONFIG.SYS.
The problem with using DRIVPARM appears to be an incompatibility with the
IBM BIOS, NOT an issue of which version of the OS!

To format a diskette, use options: /T:80 /N:9
Note that those are used by FORMAT merely to select from its existing
choices, those do NOT actually set the values of the variables (/T:70 will
NOT make a 70 track format, etc.)

> Considering the 96tpi DD 5.25" disk and the 3.5" DD disk, they have the
> same number of cylinders (80), the same number of heads (2), the same
> number of sectors/track (9), the same rotational speed (300 rpm) ,etc. So
> why isn't the capacity _exactly_ the same?

It is. The computer can't tell them apart.

Prior to DOS 3.20 (particularly in 2.11), many OEMs started using
5.25" 720K drives and 3.5" 720K drives. But because it was not sanctioned
by IBM, there was no standardization, and there were many mutually
incompatible formats. Starting with 3.20, the format is standardized.

Support for 1.4M started with version 3.30.

Fred Cisin                      cisin_at_xenosoft.com
XenoSoft                        http://www.xenosoft.com
2210 Sixth St.                  (510) 644-9366
Berkeley, CA 94710-2219
Received on Mon Jun 26 2000 - 15:58:30 BST

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