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If DEVTAB is
specified,
the
next
three
full
words
contain
the
following information:
Word 3
Word 4
Word 5
Bytes 1-2
The
numcer
of
physical cylinders on the
device.
Bytes 3-4
The number of tracks per cylinder.
Bytes 1-2
Maximurr. track length.
Byte 3
Byte 4
Byte 1
Block
Overhead
the
number
of
bytes
required
for gaps and check bits for each
keyed clock other than the last block on a
track.
Block
Overhead
the
number
of
bytes
required
for
gaps
and
check bits for a
keyed block that is the last
block
on
a
track.
Block Overhead - the number of bytes to be
subtracted if a clock is not keyed.
Byte 2
bits 0-6 Reserved
bit
7 If
1, a tolerance factor must be
applied to all blocks except
the
last block on the track.
Bytes 3-4
Tolerance
Factor - this factor is used to
calculate the effective length of a block.
The calculation
shculd
be
perforwed
as
follows:
step 1 - add the block's key length to the
block's data length.
Step
2
- test tit 7 of byte 2 of word 5.
If bit 7 is 0, perform step 3.
If
bit
7
is
1, multiply the sum computed in step 1
by the tolerance factor.
Shift the result
of the multiplication
nine
bits
to
the
right.
step
3
add
the
appropriate
block
overhead to the value obtained above.
System Macro-Instructions
127
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