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C141-E124-01EN3 - 26
a. Header
x Media type
X '00' (default type) must be specified in this field.
x Byte 2
Bits 7 and 4 of this field have meaning only in the header transferred to the INIT by the
MODE SENSE and MODE SENSE EXTENDED commands. The values specified in
these bits are disregarded in the MODE SELECT and MODE SELECT EXTENDED
commands. "0" must always be specified by the INIT in the other bit positions.
x Block descriptor length
This field indicates the length (block count) of the "Block descriptor" which follows the
header (not including the length of the "Page descriptor"). It is possible to define only 1
"Block descriptor" to the IDD, and either X '00' or X '08' must be specified in this field.
When X '00' is specified in this field, it indicates that the "Block descriptor" is not
included in the parameter list transferred from the INIT and the "Page descriptor" follows
immediately after the "Header."
b. Block descriptor
The logical attributes of the data format on the disk media are described in the 8-byte long
"Block descriptor."
Note:
The parameters in the "Block descriptor" are intimately related in the Format parameters
(Page 3) and the Drive parameters (Page 4). If the parameters in the "Block descriptor"
are changed, the INIT should also specify the appropriate values in the Format parameters
(Page 3) and Drive parameters (Page 4) to correct them.
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.