HP 82901M 5.25in 270K FDD

This is a dual 5.25" floppy drive for HP systems from the late 1970s and early 1980s.. It's HP-IB interface and Amigo protocol makes it compatible with a large number of HP computers, for example the HP 9836C Technical Computer & HP 85.

Floppy Disk Drives
The internal floppy drives are standard Shugart interface compatible drives, the example I have used Tandon TM200-2A drives. As such a drive emulator like a Gotek can be used in place of them.

The left drive has  set and the right   as described in the Tandon Manual. A Termination pack is also installed in the drive at the end of the shared cable in U2F.

Disk Structure
Double Density 5.25" disks used in the system are formatted with a LIF filesystem using 33 tracks, 16 sectors per track, and 256 bytes per sector for a total capacity of approximately 270KiB. The LIF filesystem measures usage in blocks, these disks have a total block size of 1056.

To decode flux data from a raw image of a LIF 5.25" disk, you can use the following diskdef to properly decode it disk hp.lif.40dd     cyls = 33    heads = 2    tracks * ibm.mfm         id = 0         interleave = 1         secs = 16        bps = 256    end end Note that sector's are 0 indexed requiring id = 0

Repairs - Modifications
Caps Wiki Page

2023-06

 * Large power supply capacitors reformed
 * Standoffs for right drive repaired with epoxy after damaged in shipping
 * Bearings for disk spin hub/flywheel re-lubricated after being seized
 * FAIL - Discovered right floppy drive top head is bad, replacement needed

2023-07

 * Replaced right floppy drive with Tandon TM100-2A unit from IBM
 * Note: Replacement drive was manually calibrated for track alignment after having unrelated issues.

External Projects and Software

 * LIF filesystem browser and tools
 * LIF filesystem browser and tools

Related Devices

 * HP 9836C
 * HP 98625 Disc Interface