Chuck Guzis cclist at sydex.com
Thu Jun 7 17:58:48 CDT 2007

On 7 Jun 2007 at 23:27, Tony Duell wrote:

> AFAIK they were actually 80 cylinder drives, with the normal 135tpi 
> spacing. Certainly on the double-head ones, HP formatted 77 user 
> cylinders, the last 3 were reserved for replacements for bad blocks, the 
> bad block map, etc. 

...and there were also the 300 RPM 40 cylinder 3.5" DS2D drives at 
67.5 tpi, used on a few CP/M systems as well as many inexpensive word 

There were also some 600 RPM Sony 67.5 tpi SS drives.  I think the 
Preis boxes used them.


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