Floppy Disk Drives / 8 inch / Disk Drive Parameters


A goal of my retro computing is the connection of an 8 inch floppy drive to a DOS PC. This is basically possible, but not so easy to accomplish. A hurdle are the drive parameters, since DOS actually does not know 8-inch drives. Remember, IBM (PC-DOS) has never supported 8 inch floppy drives!

config.sys und DRIVPARAM

DRIVPARAM is required whenever the floppy disk drive does not conform to the standard in which the system is installed. The command sets parameters when DOS is started to change the original DOS device drivers set.

DRIVPARM=/D:number [/C] [/F:factor] [/H:heads] [/I] [/N] [/S:sectors] [/T:tracks]

I do not want to go into all the parameters here, just the form factor index [/ F: factor]. This indicates the type of drive. The default value is 2.

The following table can be found in all DOS manuals from about Version 4.01. But here are two values missing, namely the 3 and the 4!

0 160/180 KByte or 320/360 KByte
1 1,2 MByte
2 720 KByte (3,5" disk)
5 Harddisk
6 Magnetic tape drive
7 1,44 MByte (3,5" disk)
8 Optical disk
9 2,88 MByte (3,5" disk)

However, if you look into a manual for versions 3.0 to 3.3, e.g. the Markt und Technik - Schnell PC Uebersicht (1988, page 252, ISBN 3-89090-567-6), then even the numbers 3 and 4 appear. Behold!

3 8 inch, single density (FM)
4 8 inch, double density, (MFM)

Here we have a first hint that it is basically possible to integrate 8 inch disk drives in DOS.

Diskettenformate von 8 bis 3,5 Zoll
Floppy disks
Update, 20.05.2018

First of all the hint, that I managed to connect an 8 inch drive to the PC. It is running and file access under MS-DOS works!

I have tried several times to set up an 8 inch drive in MS-DOS version 3.20 with 77 tracks using DRIVPARM (logical) or driver.sys (physical). I did not succeed! MS-DOS and FORMAT has always something to suspend with the parameters or you get the error message track 0 not found or invalid medium. This way seems to be obstructed.

Update, 27.05.2018

In the meantime I have read a lot of blogs and articles on the internet (Dave Dunfield, Herb Johnson, John Wilson - D Bit, ...). All information indicates that a native DOS access is not possible! First, it is the PC controller and/or second it is the BIOS, which makes access impossible. Among other things, it is the 512 byte/sector that is fixed in DOS. However, the 8-inch drives require either 128 or 1024 bytes per sector.

Thus, only the trick with the 1.2 MB drive and the lacking 3 tracks appears to work. This trick works fine. I have no problems in acessing, formatting, booting ... my various 8 inch drives.
Update, 11.06.2018

I have found the decisive note in the Microsoft Knowledge Base Articles that only those formatting parameters are possible, which are also supported by the BIOS! This is very important! Have a look at: Q35766: Supported Values for FORMAT /N and /T Switches.

Update, 29.05.2019

In other words, MS-DOS basically supports 8 inch drives, but only for certain OEM versions. IBM PC-DOS has never supported 8 inch floppy drives, only 5.25 inch.

MS-DOS 1.25 [SCP OEM] [SCP Cromemco S-100] (8-inch DSDD)

This is a Seattle Computer Products OEM version of MS-DOS 1.25 for the 8086 SCP Gazelle with Cromemco 16FDC Disk Controller. This archive contains the original setup disk, and a work disk in ImageDisk format. The images are for 1.2mb 8-inch floppy disk media (77 tracks, 2 heads, 8 sectors per track, 1024 bytes per sector MFM) It also includes Basic-86 Rev 5.27 8-nov-82 and Perfect Writer (must be configured first). Important: These disks are NOT for IBM PC compatible hardware or IBM PC emulators.


It is not possible to directly use (COPY, TYPE, FORMAT, DISKCOPY, ...) a 8 inch drive in MS-DOS with 77 tracks, i.e. in it's origin format (128 byte/sector or 1,024 byte/sector) without the help of other hard- and/or software!

  1. Only with the CompatiCard I/IV it is possible to use the logical 8 inch format with 77 tracks, 26 sectors/track and 128 byte/sector directly under DOS.
  2. The official DOS format with 77 tracks, 8 sectors/track and 1,024 byte/sector is only supported with UniForm-PC! You do not need a CompatiCard. Uniform-PC will do.

Meanwhile I also have a CompatiCard IV. Together with UniForm-PC 3.0b both form a perfect team.