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There were two versions of the Tandy Portable Disk Drive. Both were very similar. The drive is a a re-branded Brother FB-100.

Common features of both versions

Size, shape, weight
Batteris: 4 x AA
Wall power: 5.5mm x 2.1mm, 6vdc, center negative, 400ma (Tandy 26-3804)
Media: 3.5" DD, aka "720K" diskettes (not HD 1.44M)
Drive is single-sided. The disks may be single or double-sided, but the drive only uses one side.

Tandy Portable Disk Drive


TPDD bootstrap procedure
TPDD Operation Manual
Command Reference
Software Manual

Tandy Portable Disk Drive 2

200K in the form of 2 100K banks (still only uses one side of the disk)

TPDD-2 bootstrap procedure
TPDD-2 Operation Manual



Standard size code: FRW-8.5

Search "FRW 8.5 belt" on Google or ebay



Parts to build one cable

You will also need a pin crimper that fits AWG28 wires/pins like a good old Radio Shack 276-1595, or generic "SN-28B" sold by several different manufacurers, just pick any. They can be less than $15 on ebay

Pinouts... (until I make a diagram)

For the TPDD end of the cabel, the pin numbers used by Marty Goodman conform to the numbering on a standard IDC connector, female, 2x4, with polarity bump. (That kind of connector doesn't actually fit in the TPDD/TPDD-2, but the pinout is the same). Looking at the back of the TPDD: top-right pin is 1, bottom-right is 2, top-left is 7, bottom-left is 8. Note that most generic "Dupont" connetcor housings put the pin-1 marker in a different corner than IDC plugs do (on what we're calling pin 7). So, if you use a regular non-polarized "Dupont" connector housing, You'll have to ignore it's pin-1 marker. That's the great thing about standards, you have so many of them to choose from. ;) The connector housing in the DigiKey order above has a pin-1 marker in the correct place, or might have no mark at all (see drawing).

For the computer end, any rs232 reference shows the pinout, if you only look at the signal names and pin numbers, but ignore the physical location in most diagrams. Most diagrams will show the arrangeement when the computer has a male plug, while the M100 has a female. But the pin numbers are correct, and you can read the pin numbers right on the db25 connector and ignore any drawings to find where pin #N actually is on the plug.)


For PCs

TPDD used a double density 3.5" floppy, aka "720K" disk, but used a format that is incompatible with modern pc drive controllers. Normal MS-DOS formatted disks are written with MFM encoding, while the TPDD used FM encoding. Event using special software to read non-standard formats, you can't make a normal drive & drive controller read or write FM.

To read or write a TPDD disk from a modern machine, you need a working TPDD drive and the special RS232-to-TTL serial cable that came with it, and a "TPDD Client" software to talk to the drive over the serial connection the same way the M100 does.

There are several TPDD clients for more modern machines. Most of these are themselves also now no longer modern. For example Lap-Desk and PDD are both 16-bit DOS programs that don't work on Windows.

TpddTool Python TPDD Client

For M100/102/200

The normal way to use a TPDD is to install a "dos" on an M100. Several such dos's have been made. The drive came with a utility disk and a functional dos called "floppy". Others have been made by 3rd parties that provided more features or smaller ram footprint or more fleible installation/usage. There are also various special purpose utility programs aside from dos's.