View source for HP 82901M 5.25in 270K FDD

{{InfoboxDevice|Picture=Hp-82901m.jpg|Release Year=1980|Manufacturer=HP|Condition=Working|Model Number=82901M|Storage=5.25" DD Floppy Disks @ ~270KiB}}This is a dual 5.25" floppy drive for [[:Category:HP|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 <code>DS0</code> set and the right <code>DS1</code> as described in the Tandon Manual<ref>Page 26 of "OEM OPERATING AND SERVICE MANUAL TMIOO-l,  TMIOO-2 DISK DRIVES 48 TRACKS PER INCH" {{Archive web|url=http://www.bitsavers.org/pdf/tandon/TM100-1_TM100-2_48TPI_Operating_and_Service_Manuals_1983.pdf|name=in the Tandon Manual}}</ref>. A Termination pack is also installed in the drive at the end of the shared cable in U2F.
[[File:Hp-82901m-drive-config.jpg|none|thumb|Controllers of floppy drives from 89201A showing jumpers and termination pack setup.]]

== 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.[[File:525dd 16sector.png|none|thumb|HxC Disk map of floppy disk for 9836 showing 33 tracks with 16 sectors [[:File:52dd lif-formated-kfraw.zip|Disk Image Sample Files]]]]


To decode flux data from a raw image of a LIF 5.25" disk, you can use the following {{Archive web|url=https://github.com/keirf/greaseweazle|name=Greaseweazle}} diskdef to properly decode it<pre>
disk hp.lif.40dd 
    cyls = 33
    heads = 2
    tracks * ibm.mfm 
        id = 0 
        interleave = 1 
        secs = 16
        bps = 256
    end
end
</pre>''Note that sector's are 0 indexed requiring id = 0''

==Repairs - Modifications==
[https://caps.wiki/wiki/HP_82901M_5.25in_270K_FDD ''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==
*{{Archive web|url=https://www.hp9845.net/9845/projects/hpdir/|name=HPDir}}: LIF filesystem browser and tools
*{{Archive web|url=https://github.com/bug400/lifutils|name=lifutils}}: LIF filesystem browser and tools
==Related Devices==
*[[HP 9836C]]
*[[HP 98625 Disc Interface]]
== External links==
<references />
[[Category:Floppy Drive]]