Early 3.5" Floppy Drives

[Chuck Guzis]

On 12/15/2005 at 7:42 AM Allison wrote:

>Any PC controller that can do 720k 3.5" format can do 
>8" as it's the same data rate.  it's not what chips was 
>used it's how it was used.

Whoa.    Sorry, I couldn't let this one go by unanswered.

8" drives use a 500K data clock rate, not 250K like the DS2D 720K 3.5".  A
controller that supports 1.44M DSHD 3.5" should do just fine on 8". While
there were early 8" drives that used a lower clock rate, they were pretty
much gone by the time of the dawn of the PC.  FM support with a modern
controller is a somewhat different kettle of fish.  The nearest AT medium
to the 8" drive would be the 5.25" high-density diskette, which also spins
at the same rate--360 RPM.
 
That was the beauty of the NEC APC line--from 8" right down to 3.5", the
data format didn't vary one iota.  The NEC 9801 floppies still record 1.3MB
on a 3.5" drive spinning at 360 RPM.

But the  PC-XT 8" drive controllers were a special beast, honest.

Cheers,
Chuck