Data Format
(1)Block address of user space
The logical data block address number is consecutively assigned to all of the data blocks in the user space starting with 0 to the first data block.
The IDD treats sector 0, track 0, cylinder 0 as the first logical data block. The data block is allocated in ascending order of addresses in the following sequence (refer to Figure 3.5):
1)Logical data blocks are assigned in ascending order of sector number in the same track.
2)Subsequent logical data blocks are assigned to sectors in every track except the last track in ascending order of track number in the same track (head). Within the same track, logical data blocks are assigned in the same way as step 1).
3)Subsequent logical data blocks are assigned to sectors in every track except the last track in ascending order of track number in the same cell. Within the same track, logical data blocks are assigned in the same way as step 1).
4)For the last track in the same cell, subsequent logical data blocks are assigned to sectors other than spare sectors in ascending order of sector number.
5)After blocks have been assigned in the same cell according to steps 1) to 4), subsequent logical data blocks are assigned in ascending order of cell number in the same way as in steps 1) to 4). Logical data blocks are assigned starting from track 0 in the next cell until the last cylinder (immediately preceding the alternate cylinder
When the logical data block is allocated, some sectors (track skew and head skew) shown in Figure
3.5are provided to avoid waiting for one turn involving head and cylinder switching at the location where the track or the head is physically switched.
See Subsection 3.3.2 for defective/alternate block treatment and the logical data block allocation method in case of defective sectors exist on the disk.
(2)Alternate area
Alternate areas in the user space (spare sectors in the cell and alternate cylinders) are not included in the above logical data block addresses. Access to sectors which are allocated as an alternate block in the alternate area is made automatically by means of IDD sector slip treatment or alternate block treatment (explained in Subsection 3.3.2), so the user does not have to worry about accessing the alternate area. The user cannot access with specifying the data block on the alternate area explicitly.