Re: Disk II Phase Question

[mjmahon@aol.com (Michael J. Mahon)]

Jplcsch wrote:

>Look the routine of  flight simulator II, it's really the maximum you can
>put on a track (18 pages with a small amount for the translation table!)
>on look the track with CIA or any other utility
>to help you:
>Syncro are $FE
>start of track $D5 $AA $D5
>after you found a transalation table
>a close byte $94
>the marker of every sector (just one) $D5
>18 pages  (if you unassemble the read routine you'll found a loop with $12
>to test the nb of sectors read on the track)
>checksum
>close markers for the track $DE $AA

I'm not sure what you mean by a "translation table".  The nibble
translation table is usually generated, not written on the disk.
If it were written, it would be 256 bytes long.

Are you refering to something else?

And is there no check byte?

I note that the 18-page format you describe above requires 6172
nibbles (of which perhaps 5-10 have two extra bits).  That works
out to 193.5 milliseconds, or a little more than 3% less than 200 ms.,
meaning the writing drive could be a little more than 3% fast and
still work.

Since the read routine can handle a writing drive at least 5% slow
and a reading drive at least 5% fast, there is room for one more
"page" of nibbles on a track if the writing drive is set 5% slow.
(Another page would need only 5.5% more nibbles on a track.)

Such a format could only be written a track at a time, but would
provide a 19% disk capacity boost over the standard format.  ;-)

-michael

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