Xerox 820-II diskette formats

Chuck Guzis cclist at
Mon May 4 10:48:34 CDT 2009

On 4 May 2009 at 10:14, js at wrote:

> Steven Hirsch wrote:
> > On Sun, 3 May 2009, Chuck Guzis wrote:
> >> The 820-II 8" samples in my library show 77*1*26*256 and
> >> 77*2*26*256 formats.
> > That's fairly conservative, but works out to almost a 1MB for the
> > DSDD diskettes.  Most systems I'm familiar with formatted at 32 x
> > 256 in DD mode.
> What?!   Using what controller chip?  How that's even possible while
> maintaining the same 360rpm?

The only time I've ever seen 32x256 on an 8" track it's been with 
hard-sectored media.  I do have a 30x256 8" format in my library 
(Lobo) but nothing more than that.  OTOH, 16x512 is quite possible 
and used by several systems, including  Tandy and Zenith.


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