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C141-E205 3-13
(2) Alternate block allocation by REASSIGN BLOCKS command
When the REASSIGN BLOCKS command is specified, the alternate block is allocated to the
defective logical data block specified by the initiator by means of alternate sector treatment. The
alternate block is allocated to unused spare sectors in the alternate cylinder.
Figure 3.8 is examples of the alternate block allocation by the REASSIGN BLOCKS command.
Example Reassign: Block 16.
: Unused spare sector
: Defective sector
: n represents a logical data block number
Figure 3.8 Alternate block allocation by REASSIGN BLOCKS command
(3) Automatic alternate block allocation
• Automatic alternate block allocation at read operation
If the ARRE flag in the MODE SELECT parameter permits the automatic alternate block
allocation, the IDD automatically executes the alternate block allocation and data duplication on
the defective data block detected during the READ or READ EXTENDED command. This
allocation method is the same as with the REASSIGN BLOCKS command (alternate sector
treatment).