13 Mar
2005
13 Mar
'05
8:11 p.m.
Megan wrote:
What you need to understand is that RT-11 has a maximum
volume size
of 65536 blocks. Therefore, for volumes which are larger than
this (typically only the DU drives, like RD53 and RD54, or SCSI or
DSSI which act like MSCP devices), the drive is logically partitioned
into units of 32mb each...
Jerome Fine replies:
I am pleased you note that each RT-11 partition is
65536 blocks - except maybe (usually) for the last
RT-11 partition. It is again helpful to note that
internally, RT-11 reports the size as 65535 blocks
with the first block being zero and the last block
being block 65534. This is so that a full 16 bit
word can hold that largest size of 65535. blocks
even though the actual size is 65536. blocks.
If anyone thinks to test the above information, try:
COPY/DEVICE DU0:/START:65535./END:65535. DU1:/START:65535.
or any other block for DU1: for that matter. NOTE
that any other "START" block number for DU0: will result
in the END block 65535. not being used. This is because
there is a bug in DUP.SAV which ignores block 65535. except
when there is ONLY a single block to copy. In that case,
I presume that the person who wrote the code forgot to
check that block 65535. should also be ignored in that
case as well. I conclude that the likely reason is that
2 mistakes resulted in what the user requested being done.
For example, try:
COPY/DEVICE DU0:/START:0./END:65535. DU1:/START:0.
the result is the same for both of the following:
COPY/DEVICE DU0: DU1:
COPY/DEVICE DU0:/START:0./END:65534. DU1:/START:0.
with NO warning message being provided in the last
case.
Sincerely yours,
Jerome Fine
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