[sebhc] h17 and h8d disk images

[Dave Dunfield]

> I see your point from this perspective as well. I think that
>CP/M chose this route because at the time some disk controllers
>were not able to generate interleaved disk. In order to improve
>perfomance, they chose to deal with it this way. ( I have just
>such a controller on my IMSAI ).
>Dwight

Thats exactly it - any soft sectored system, and any hard sectored
system which records the sector number in a "soft" header (like the
H17) can do "physical interleaving" - which I far prefer above "logical
interleaving" because it avoids an extra translation level.

Although it would be technically possible to enforce sequential sector
numbering in a soft system, I have never seen it done - the controller
just waits until the right header comes along (otherwise soft read
errors on headers before the one you wanted would cause a retry).

Unfortunately, systems like the NorthStar SD one I described in an earlier
message which physicallt tie the sector numbering to the physical sector
index holes cannot do this, and would require a translation if you wanted
to be able to do interleave.

Given a controller like the H17 which is capable of "physical" interleave,
I would prefer to do it that way, and leave the CP/M sector translation
table at 1:1 - this makes more sense to me, and moves the entire interleave
issue into strictly a formatting concern (where it should be) - once formatted,
no special action has to be taken, no matter what the interleave factor of
the diskette is.

Regards,
Dave
-- 
dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Vintage computing equipment collector.
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