This is a clarification of the DiscOp interface.
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This document clarifies the job required of filing systems registering
themselves with FileCore.

Miscellaneous Reason 0 (Mount)
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The filing system should:
i) Identify the disc's format, using the parameters supplied by FileCore as
        a first guess.
ii) Fill in the supplied disc record with the disc's format. The fields to
        fill in are: Log2 of sector size; sectors per track; heads;    
        density; Low sector.
iii) Read the requested data off the disc.

The number of heads to fill in is the actual number of heads present. It is
up to FileCore to adjust this and the sequencing flag for subsequent
operations.

If the number of bytes per sector are 256 or less (Log2 sector size <= 8)
then fill in the number of heads-1 into the heads field, otherwise fill in
the actual number of heads.

The values to fill into density are:
        1 - single density
        2 - double density
        4 - quad density

 - the double step and side sequencing flags in this
                byte should be set to 0.

FileCore will subsequently correct the side sequencing flag depending the
sector size. Note that this is simply used as an initial value.

DiscOp restore
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The disc address is only used for the drive number. The bottom 29 bits may
be junk.

