Table of Contents
Advertisement
2.9.2 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, 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 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.
C141-C009
2.9 Data Block Addressing
2-23
Advertisement
Table of Contents
