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Command Specifications
3 - 24 C141-E167
If only the "Block descriptor" in this command is changed, the IDD changes the values in
the "Sector count/track," Data byte length/physical sector," "Track skew factor" and
"Cylinder skew factor," as well as the "Cylinder count" value in the drive parameters (Page
4) in accordance with the contents specified in the "Block descriptor," and uses the
"Current" values as is for the other parameters.
• 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 accessible data block count can
be limited without formatting if "Data block count" value is within a "Cylinder count" value
of page 4. "Cylinder count" value is not changed until the IDD is formatted. If a value
exceeding the data block count obtaining from the "Cylinder count" of page 4 is specified,
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 as 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 IDD retains its current capacity, if the block size or alternate sector count has not
changed. If the "Data block count" is set to zero and the Data block size or alternate sector
count has changed, the IDD shall set to its maximum capacity when new block size or
alternate sector count to be effect.
• 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 (4-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 the number except the multiple of 4 is
specified within this range, the number is rounded up at the multiple of 4 that is closest to
the specified number. (Rounding processing is reported.)
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.