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Tandy Portable Disk Drive

There were two versions of the original Tandy Portable Disk Drive, "26-3808 Tandy Portable Disk Drive" or now called "TPDD1", and "26-3814 Tandy Portable Disk Drive 2" or "TPDD2". Both were very similar.

The original TPDD1 is a re-branded Brother FB100. In fact the Brother FB100 was sold under several names. At least:

Brother FB100
TANDY Portable Disk Drive
knitking FDD19
Purple Computing D103

The TPDD2 was also sold under multiple names. At least:

TANDY Portable Disk Drive 2
XOB Disc-88

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


Operation Manual
Software Manual
Service Manual
TPDD1 bootstrap procedure
Command Reference

Tandy Portable Disk Drive 2

200K, in the form of 2 100K banks

TPDD2 Operation Manual
TPDD2 bootstrap procedure
TPDD2 Sector Access



Standard size code: FRW-8.5

Search "FRW 8.5 belt" on Google or ebay


You can't buy the original special cable any more, but there is a new one you can buy, or you can build one for yourself.

The "RS-232C" interface to the TPDD is actually 5v TTL (0v to +5v), while RS-232 serial ports use -12v to +12v. So the cable isn't just a cable, it has electronics inside the DB25 plug to convert the signal levels between TTL and RS-232.


|                                                |
|                                                |
|                 RS-232C                        |
|                   ___                          |
|               +--+   +--+              +-----+ |     
|               | 7 5 3 1 |              | (o) | |
|               | 8 6 4 2 |              |     | |
|               +---------+              +-----+ |
8 EB+ (External Battery +4.8 to +6v) (Only on TPDD2, n/c on TPDD1)
TPDD2 original cable.jpg


Software related to these drives can be broken into 2 main categories, clients and servers.

A TPDD client (aka dos) is software that uses a TPDD drive. This includes TS-DOS, and the program called "Floppy" which came on the special disk that came with the TANDY versions of the drives.

A TPDD server (aka emulator) is software that pretends to BE a TPDD drive. This includes LaddieAlpha, dlplus, and others.

Misc Related Info

TS-DOS implements an extension to the TPDD protocol to provide subdirectories.
A real TPDD or TPDD2 doesn't support this, but some TPDD emulators do (NADSBOX, PDDuino, dlplus, LaddiAlpha at least)

TS-DOS Directories

TPDD uses standard 720k DD 3.5" disks, but uses a format that is incompatible with modern pc drive controllers.
Normal MS-DOS formatted disks are written with MFM encoding, while the TPDD uses FM encoding.
Even using special software like TeleDisk to read non-standard track/sector formats, you can't make a normal drive & drive controller read or write FM. An old pc with an early floppy controller chip and an old 720k drive may be able to do it.

To read or write a TPDD disk from a modern machine, you need a working TPDD drive, the special RS232-to-TTL level-shifting serial cable, a 9F-to-25F straight through (not null-modem) serial adapter or combination of cables & adapters, and TPDD client software to talk to the drive over the serial connection the same way the M100 does. See, PDD.EXE, or from the TPDD clients link above.

Don't use 1.44M HD disks in a TPDD. Use 720K DD disks.