Xerox 820-II diskette formats

[Chuck Guzis]

On 5 May 2009 at 11:08, js at cimmeri.com wrote:

> So clarify this for me.   Someone figured that they could squeeze more
> out of a track than the IBM System 34 standard?  How was this done? 
> By decreasing decreasing the gap lengths?

Exactly.  After all, IBM did it--the original 160K 5.25" disks for 
the 5150 were 8*512 and by DOS 2.0 had been expanded to the 9*512 
180K format.  It's possible to reliably fit 10*512 on a 2D 5.25" 
diskette on a PC with reasonably "modern" drives, but the gaps get 
very small.  Many CP/M formats left off the IDAM to make room for 
larger gaps when the 10*512 format was used, but that's not an option 
for a stock 765-based controller.

On an 8" drive, the limit is 30 sectors for the 256 byte soft-sector 
floppies.

Cheers,
Chuck