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2.9 Data Block Addressing
C141-C013 125
2.9.2 Logical block addressing
The HDD 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
HDD 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 HDD makes cylinder 0, track 0, and 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 in accordance with 1) and 2),
starting from the same head allocated from the last logical data block cell
immediately prior to the next cell head logical data block.
6) Henceforth, with each cell switching, the head is switched between ascending
order and descending order, and logical data blocks are allocated accordingly.
Up to the last cell of the relevant zone, succeeding logical data blocks are
allocated sequentially according to cell numbers.