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Data Format
3-12 C141-E163
(1) Alternate block allocation during FORMAT UNIT command execution
When the FORMAT UNIT command is specified, the allocation of the alternate block to those
defective sectors included in the specified lists (P, G, or D) is continued until all spare sectors in the
same cell are used up. When they are used up, unused spare sectors in the alternate cylinder are
allocated to the subsequent sectors in the cylinder by means of alternate sector treatment. Figure 3.7
is examples of the alternate block allocation during the FORMAT UNIT command execution.
Figure 3.7 Alternate block allocation by FORMAT UNIT command
If the data block verifying operation (certification) is not permitted (DCRT flag = 0) in the FORMAT
UNIT command, the IDD checks all initialized logical data blocks by reading them out after the
above alternate block allocation is made to initialize (format) the disk. If a defective data block is
detected during the check, the IDD allocates the alternate block to the defective data block. This
alternate block allocation is made by means of alternate sector treatment only like processing by the
REASSIGN BLOCKS command even if unused spare sectors exists in the same cell.
: Unused spare sector
: Defective sector
: n represents a logical data block number