HP 9816 CP/M-68K

Chuck Guzis cclist at sydex.com
Mon Feb 12 15:18:29 CST 2018

On 02/12/2018 12:23 PM, Fred Cisin via cctalk wrote:
>> Imagedisk can't handle mixed sector sizes on a track.
> Reading or writing multiple sized sectors can be done with multiple passes.
> But, I don't know how to FORMAT a track with multiple sector sizes with
> NEC 765 type controller.  Not as hard with WD style controllers.

It's actually not too difficult.  There were DOS utilities that could,
for example, copy IBM XDF format.

The trick is that on the 765 and its ilk, the FORMAT command writes
sector headers according to the length parameter in the *command*,
whereas the WRITE SECTOR command writes things out according to the
length in the sector ID header.

So, for example, you can specify that, say, 18 256 byte sectors are to
be formatted, but each ID header would have a code of 3 or 1, indicating
that the data part of the sector is 1024 or 256 bytes.  Pick the
appropriate sectors to write and you'll clobber any of the 256 byte ones
that fall under the 1024 byte shadow of the larger ones.

It does take a bit of planning, but it does work.

In fact, this is a handy way to "wipe" a track free of any ID
information at all.  Just format up a couple of sectors with a length
code of 6 or 7 and then write them.  They'll eat their own heads,
ignoring the index.


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