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.

Both of the drives are jumpered at  on U1E, 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