FUJITSU MAG3091FC - Manual (Page 44)

C141-E078-02EN 3 - 13
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 generates the C list for defect location
information and 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 cylinder.
: Unused spare sector
: Defective sector
: n represents a logical data block number