Retro-Computing Floppies


Retro-computing Interface Machine

I have a machine dedicated to working with floppies. It’s your bog-standard Pentium-class machine from the 1990s, but with a few additions (newer and older).


Catweasel vs Kryoflux

EPROM Burner



Converting Disk Formats

Converting disk images becomes a maze of twisty little passages, all alike.

src / dstrawTeledisk (.TD0)ImageDisk (.IMD).DMKJV (.DSK)
Teledisk (.TD0)-
ImageDisk (.IMD)IMDU-
JV (.DSK)[2][1][3]-

1 Reportedly, openMSX has Current 0.9.1 version does not. 2 TRSREAD / TRSWRITE can read/write files to/from DMK and DSK. 3 Tim Mann’s dmk2jv3 and jv2dmk

Great catalog of tools at


720k image won’t mount on Linux

I want to get the actual files off a disk; I don’t care about the physical format. I ran IMDU.COM on a 720k ImageDisk file to create a binary image. When trying to mount the raw image on Debian Linux, I got an error:

# mount -t msdos -o loop image.bin /mnt
FAT: invalid media value (0xed)
VFS: Can't find a valid FAT filesystem on dev loop0.

Used FreeBSD instead: # mdconfig -f image.bin md0 # mount -t msdos image.bin /mnt

8” Disks



  1. ImageDisk: Open source, documented replacement for Teledisk, by Dave Dunfield.
  2. TeleDisk

Teac Drive Naming

Teac drive coding (the letter after the number) is fairly specific. Combinations of letters mean that the drive can support both types of media. The numbers before the letter dictate the physical size of the meidum. Letters and numbers after that indicate other features (e.g. right-hand latch lever, locking mechanism, head-load solenoid, bezel color, electronics version, SCSI interface, etc.).

The more common capacity letters are:

  • B = 360K (DS2D)
  • F = 720K (DS2D)
  • G = 1.2MB (DSHD)
  • H = 1.44MB (DSHD)
  • J = 2.88MB (DSED)

The common size codes run as follows:

  • 35,135,235,05 = 3.5”
  • 5, 45, 55, 155 = 5.25”

So the bog-standard 360K 12 height 360K drive is the FD55B. The usual 1.2MB drive is FD55GF (because it supports both 1.2M and 720K formats). A half-height 5.25” 720K drive is an FD55F. A third-height 720K 3.5” drive is a FD23F; a 3-mode (720, 1.2M, 1.44M) one-third hieght 3.5” drive is an FD235HG. A 2.88MB 3.5” drive is an FD235J.

What you have is 720K (96 tpi, 300 RPM) drive. You can use it by declaring in your BIOS setup that it’s a 3.5” 720K drive, but you’ll be writing disks that few can read. The 720K format with a 1.2MB floppy is thwarted by the PC BIOS because it double-steps the head to simulate a 360K format (which is why 360K disks formatted or written in a 1.2MB drive often can’t be read in a real 360K drive). Further, the PC BIOS expects a 360 RPM drive for the low density mode.

Updated January 1, 2013