Re: CP/M disk format question

[pausch@saaf.se (Paul Schlyter)]

In article <q9OdnSOzyvqENurVnZ2dnUVZ_trinZ2d@comcast.com>,
Bill Garber <willy46pa@comcast.net> wrote:
>
>"Paul Schlyter" <pausch@saaf.se> wrote in message news:g588c2$28ac$1@merope.saaf.se...
>> In article <48779f9e$0$17148$742ec2ed@news.sonic.net>,
>> Andy McFadden  <fadden@fadden.com> wrote:
>> >All of this is in the context of Apple II CP/M on a 5.25 floppy.
>> >
>> >CP/M disks use 1K blocks, and have a directory starting at block 12 (track 3
>> >on a 5.25" disk).  The first 3 tracks are reserved for the boot image.  That
>> >leaves 140K - 12K = 128 blocks.
>> 
>> All of those quantities are actually configurable - their values are
>> stored in the DPB (Disk Parameter Block) in the BIOS, where each disk
>> has its own DPB.
>> 
>> I hooked up 80 track DSDD disks to my Apple II in the 80's and made
>> all of the disk into a 640K CP/M disk volume.  Then I had to make the
>> CP/M blocks 2K large, since a CP/M disk with 1K blocks cannot be as
>> large as 640K.
>
>
>Paul, 
>
>I read this somewhere before. 
>Is/was it documented on your site at one time? 

No, I never documented it there.  But the format and contents of the DPB
is documented in the "CP/M Alteration Guide", published by Digital
Research in the late 1970's.  Then you must also modify the CP/M
RWTS a little, and finally, an extra signal was needed to choose which
head of the floppy to use - I used one of the annunciator outputs on
the game port of the Apple II for that.

>Bill Garber from GS-Electronics
>http://www.garberstreet.com
>
>


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