3.5" floppy drive question(s)

[Phill Harvey-Smith]

Curtis H. Wilbar Jr. wrote:
> 
> Was wondering if 3.5" HD floppy drives can be jumpered/used in
> a system that only supports 720K, using them as 720K only
> drives ?
> 
> I only own one 720K floppy drive (wouldn't mind a few more).
> 
> If that is possible, and only possible with some drives, anyone know
> if it is possible with any of the following:

Standard PC 1.44M drives will work fine as 720K drives as long as you 
ONLY use 720K DD media, most drives auto detect the media and adjust the 
data rate accordingly. The same is not true however for 1.2M 5.25" 
drives which IIRC must be told what rate to operate at, as the spindle 
speed is higher for 1.2M, and there is no density select hole as there 
is on 720K/1.44M.

There are a couple of problems however, most 1.44M drives are jumpered 
to operate as drive 1 only, and cannot easily be changed, this can be 
fixed however by swapping lines in the cable e.g. swapping 10 and 12 
will make the drive respond as drive 0.

Also depending on your system, it may require a ready signal on Pin 34, 
most 1.44M drives supply disk change on this pin, however the couple of 
systems I have worked with that require this signal (Amstrad CPC, 
Spectrum +3), wiring the signal permenently to ground will do the trick.

Note some of the older 1.44s may have jumpers to change the ID, and 
enable ready. I have some Teac FD-235F drives that are like this (they 
have a bunch of jimpers just to the left of the steper motor), 
unfortunatly the HF that you have does not.

> Also, anyone know if there if it is possible to slow the spindle speed
> so that 1.44M can be done on machines that only have DD data rate ?
> (and if so, any of the above drives capable of being slowed ?)  Would
> that even work ?

Unfortunatly I believe that the spindle speed in 1.44s is always 300rpm, 
even when operating in HD mode, and that is fixed in the drive, I don't 
think that's possible (with standard drives at least).

Cheers.

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.