Early 3.5" Floppy Drives

[Allison]

Fred Cisin wrote:
> On Thu, 15 Dec 2005, Allison wrote:
> 
>>765A write clock rate by drive and density, bit rate is clock/2.
>>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)
> 
> 
> one more entry to add to that table:
>   5.25    "HD"     MFM    1000KHz (1.2M) (looks like 8", could be SAME CHS)

I wanted to leave that sick puppy out of it (along with 2.88mb).

The CHS could be the same, save for 8" DD was often different.

>>None of this has anything to do with rotation rate of the media.
> 
> Very true.  8" and "1.2M" is 360RPM, all others are 300 RPM,
> with a few exceptions (early Sony 3.5 at 600 RPM, NEC, Weltec, etc.)

It sounds upside down to me.  The 300rpm 1.2mb gets you a standard data rate
500kbS(1mhz clock) and the 360 gets you the 600kbS rate (1.2mhz clock).
I really try to shun that pile from my mind.

the general game with spindle speed was one of to cases, lower latency
(spin faster) or play games with data rate without altering the controller 
logic.  Maybe even both. No question a 600rpm spindle would get your data 
around sooner.


Allison