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1.8.2 Logical block addressing
The IDD uses logical data block addressing which is not dependent on the disk drive’s physical
structure as the method of data access on the disk medium. The IDD makes correspondence between
each physical sector and each logical data clock address during formatting. Access to the data on the
disk medium is performed in logical data block units and the INIT specifies the logical data block
address that is its object during access.
In logical data block addressing, specifying of a data block address is a function which specifies 2
continuous binary numbers for each drive. Furthermore, the INIT can know the logical data block
address range in the user space where specification is possible using the READ CAPACITY
command.
(1) User space logical block addresses
The top data block in the user space is made logical data block address “0,” then continuous logical
data block addresses are allocated to each data block until the last data block in the user space.
The IDD makes cylinder 0, track 0 sector 0 the top logical data block, and allocates subsequent
logical data blocks in the order described below to addresses in ascending order.
1) Within the same track, logical data blocks are allocated to sector numbers in ascending order.
2) Within the same head of the same cell, succeeding logical data blocks are allocated to the sectors
in each track according to 1) in the ascending order of cylinder numbers.
3) Within the next head of the same cell, succeeding logical data blocks are allocated to the sectors
in each track according to 1) and 2) in the ascending order of track numbers.
4) On the last track inside the same cell, succeeding logical data blocks are allocated to sectors
except for spare sectors according to 1).
5) After all the allocation in 1) to 4) is completed within the same cell, succeeding logical data
blocks are allocated to the next cell beginning with track 0, according to 1) to 3), and so on to
each cell number in ascending order until the last cell in each zone (refer to alternate cell b-1 in
Figure 1.5) in the user space, with the exception of alternate cells.
(2) Alternate area
The alternate area in user space (spare sectors within each cell and alternate cells) are excluded from
the abovementioned logical data block addresses. Access to allocated sectors as alternate blocks
within the alternate area is performed automatically by the IDD’s defect management (sector slip
processing and alternate block processing), so it is not particularly necessary for the user to access
the alternate area. Also, data blocks in the alternate area cannot be clearly specified and accessed
directly.