10 Oct
2007
10 Oct
'07
8:53 p.m.
On Wed, 10 Oct 2007, Fred Cisin wrote:
If you find alternating 00 and numbers, then it is
normally a sixteen bit
number. If a program is wrong about THAT, then it will think that block 0
is being crosslinked many times.
Can't speak for CDOS, but in CP/M block zero contains the first block of
the directory; it can't be allocated to a file. Disk allocation is kept
in a bitmap in memory, with one bit per block (I'm talking 2.x here; I
think 3.0 used two bits per block, but I'm not up on 3.0). The BIOS
indicated which blocks were allocated to the directory by supplying the
first 16 bits of the allocation bitmask, making block 0 the first block
of the directory. Since there must always be at least one block in the
directory, block 0 can't be allocated to files.
Of course, I may be wrong; wouldn't be the first time.
--
roger ivie
rivie at ridgenet.net