2.4 Megabyte Floppies

Fred Cisin cisin at xenosoft.com
Sat Sep 9 16:02:11 CDT 2006

> >They have a two speed spindle 360/180 rpm and use 500kbit mfm just like
> >8" dd disks. 2.4 meg. only works on "microcode" disks though. And they are
> pretty
> >scarce.

On Sat, 9 Sep 2006, Chuck Guzis wrote:
> This reminds me of one of the dodges offered early on in the PC to enable a
> 5150 or 5160 PC to handle 1.2M diskettes without swapping the controller
> card--someone offered a dual-speed drive that spun at 300 and 180 RPM (not
> to be confused with the 300/360 dual-speed 1.2M drives).  Apparently it
> worked, but I wondered how good the S/N ratio at the lower spindle speed
> was.

Weltec was the best known of those.  180RPM drive designed for 600 Oersted
media at 250K data transfer rate.  I know somebody who has one (if he can
find it).  It worked, but reliability was noticeably lower than the real

At the 500K rate, it should work for the 2.4M.
But so would a "normal" 1.2M drive run at a 1000K data transfer rate

> For a short time, it was either very expensive or next to impossible
> to get a 1.2MB-capable controller for a 5150, since the PC/AT put the FDC
> on the HDC board.  The gap was quickly filled by outfits like Micro
> Solutions and Sysgen (and then the Far East cloners) and the dual-speed
> drives vanished.

I had 8" drives on 5150 before I had an AT.
Flagstaff Engineering, MicroTech Export, Vista, Maynard, Amlyn, Tall tree
(JDisk), etc.
Before the AT came out, there wasn't a solid standard for how mode
switching was controlled.  And, before the AT, some of the 1.2M drives had
a 50 pin 8" style connector.

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