Early 3.5" Floppy Drives

Roger Merchberger zmerch at 30below.com
Thu Dec 15 12:40:44 CST 2005

Rumor has it that Allison may have mentioned these words:

>Size   density  format   writeclock
>8"       DD      MFM     1000khz
>8"       SD       FM      500khz  (8"SSSD 241k CP/M standard)
>5.25     DD      MFM     500khz (40track is 360k, 80track 720k)
>5.25     SD       FM     250khz
>3.5"     HD      MFM    1000khz (1.44mb) (looks like 8" different CHS)
>3.5"     DD      MFM     500khz (720k)   (same rate as 5.25 DD and 8" SD)
>3.5"     ??       FM     250khz (not used obsolete)

3.5" FM was used for microcomputers - the Tandy Portable Disk Drive (OEMmed 
by Brother, IIRC) was 40 tracks, 2SPT FM w/100K storage. Serial port 
driven, and worked with the Tandy Model 100/102/200 laptops. In my Service 
manual for the critter, it did mention the density, but I don't have that 
handy. DD disks worked just fine on it (read: data life at least into the 
10 year range), but HD didn't work so well, IIRC.

The TPDD2 was also FM, but used an 80 track drive (set into 2 banks for 
compatibility with the TPDD1) for 200K storage.

Roger "Merch" Merchberger

Roger "Merch" Merchberger  --  SysAdmin, Iceberg Computers
  _±±_                          zmerch at 30below.com
(©||®)  If at first you don't succeed, nuclear warhead
  _)(_   disarmament should *not* be your first career choice.

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