C141-E039-01EN
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Data Block Count
This field specifies the total number of logical data blocks (the block length is
specified in "Data block length) allocated in the "User Space" on the disk media. The
maximum logical block address is a value with 1 subtracted from the value in this
field.
The "Data block count" has an intimate relationship with the specifications on Pages 3
and 4.
If only the "Block descriptor" in this command is changed, the "Cylinder count" on
Page 4 is set to a realizable cylinder count which takes into account the "Alternate
track count/drive" and "Alternate sector count/zone" components in Page 3 resulting
from the value specified here (no rounding processing report is made). If this cylinder
count exceeds the maximum cylinder count that can be use din the User Space, the
"Data block count" is rounded to the maximum value that is realizable. (there is a
rounding processing report in this case).
If zero is specified for the "Data block count," or when the block descriptor is not
specified, the total number of blocks that it is possible to use after the "Alternate track
count/drive" and "Alternate sector count/zone" components in Page 3 are subtracted
from the "Cylinder count" on Page 4 is set in the "Data block count" (rounding
processing is not reported).
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Data Block Length
This field specifies the byte length of a logical data block on the disk media.
The logical data block length and physical data block length are the same in the IDD.
The data block length can be specified at 512 to 528 bytes (2-byte boundary).
If less than 512 bytes is specified in this field, the IDD performs rounding processing
(there is a rounding processing report), setting the data block length at 512 bytes. If
more than 528 bytes is specified, rounding processing is performed (there is a
rounding processing report), setting the data block length at 528 bytes. If an odd
number is specified within this range, rounding processing is performed which adds
+1 to the specified value (there is a rounding processing report).
If zero is specified in this field, the value specified in bytes 12 and 13 (Data byte
length/sector) of Page 3 (Format Parameter) is set. At that time, if Page 3 is not
specified at the same time, the current value in Page 3 is used.
If the value set in this field differs from the value specified in bytes 12 and 13 (Data
byte length/sector) of Page 3 (Format Parameter), the data block length in the block
descriptor is set.