[sebhc] h17 and h8d disk images

Barry Watzman Watzman at neo.rr.com
Wed Sep 1 18:45:48 CDT 2004

There are two ways to interleave.

In the 1st method, used by CP/M, you have an interleave table in the
operating system itself.  The sectors are in physical order on the diskette,
but are not used in physical sequence.  That is, CP/M (on an 8" disk) uses
sector 1 then 7 then 13, then 19, etc.

The other way is to have the OS use the sectors sequentially (1,2,3 etc.)
but to do the interleaving when the disk is formatted.  So the OS will ask
for sector 1, 2, 3 ...., but on the disk the sector after sector 1 is not 2
but rather something else.  There is no requirement that the sectors on the
disk be in sequential order.  In fact, there is no requirement that they be
contiguous, or that they be "positive" numbers (if one wants to interpret
them as signed numbers).  They are more like labels than actual numbers,
they can be in any sequence, and there can be gaps (a fact on which may copy
protection schemes rely).

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