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3-12 C141-E198
(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
During FORMAT UNIT command, alternate block allocation is conducted in following cases:
1) Unrecovered write offtrack condition during a media write
2) Uncorrectable Data Error during a media read (certification) *1
If above errors are detected during FORMAT UNIT command, the IDD allocates the alternate
block(s) to the defective data blocks. Reassign procedure itself is the same as one in REASSIGN
BLOCKS command.
: Unused spare sector
: Defective sector
: n represents a logical data block number