Amdek 3" Floppy Drives

[Tony Duell]

> The discussion of 3.5" floppies probably wouldn't be complete wtihout
> mentioning HP.  What follows is a case of IIRC.
> 
> Sony had originally brought the 3.5" drives out as 40 track 600 RPM
> drives.(OAD-1).  While impressive with their shorter latency, the 600 RPM

Hmmm.. The original Sony drives were certainly 600 rpm units, but I 
thought 80 cylinder ones were there from the start. There are 40 cylinder 
3.5" drives (67.5 tpi), in fact I've just been working on one (the Epson 
PF10 floppy drive unit for the PX8). I haev never seen a 600 rpm 40 
cylinder unit, though

> drive was not compatible with existing controllers.  HP adopted the Sony
> 3.5" format but standardized on a 300 RPM 80 track drive.

No. NP used 600 rpm drives. Both the 'original' full height ones with a 
26 pin connector, as used in the 9121, 9122, 9123, 9133, 9114A, etc and 
the half-helght ones used in the 9153 and 9114B. I am absolutely sure of 
this (darn it, enough of them have passed my bench :-)).

Remember that HP drive untis were intellegent, they included the 
controller, and communicated to the host via an HPIB or HPIL link. It 
didn't actually matter what speed the disk turned at (the bit density is 
the same on an HP 600 rpm disk as on a normal PC disk). 

IIRC, HP only used 70 cylinders on single-sided units and 77 cylinders on 
double sided units for user data. The remainder were used to replace bad 
tracks (!). This was handled by the drive unit (HP's controller board) 
rather than the host.

I suspect that all HP PC clones had 300 rpm drives, though.

-tony