6.1 Defect ManagementC141-C009 6-3c. Alternate block allocation processingAlternate block allocation processing is implemented by the FORMAT UNITcommand, REASSIGN BLOCKS command or "Auto Alternate BlockAllocation Processing." In sector slip processing, the defective sectors reexcluded and logical data blocks are located in physically consecutive sectors,but when alternate block processing is performed, the affected logical datablocks are located in spare sectors which are not physically consecutive withthe previous and following logical data blocks which are physically locatedon the disk.− Alternate block allocation processing during FORMAT UNIT commandexecutionWith the FORMAT UNIT command, alternate block allocation is doneby sector slip processing until all the spare sectors within the same cellhave been used up for defective sectors included in the type of defect list(P, G or D) specified in the command. When all the spare sectors in thesame cell have been used up, subsequent defective sectors in that cell aretreated by allocating spare sectors in an alternate cell by alternate sectorprocessing.After implementing this alternate block allocation and initializing thedisk media, at times when a data block Verify (Certification) operation isnot prohibited, the IDD, reads all the initialized data blocks and verifiestheir normalcy. If a defective data block is detected during thisprocessing, the IDD generates the C List as defect position informationand allocates alternate blocks by alternate sector processing for thosedefective data blocks. In this case, alternate blocks are allocated in sparesectors in an alternate cell.− Alternate block allocation processing by the REASSIGN BLOCKScommandWith the REASSIGN BLOCKS command, alternate block allocation isperformed by alternate sector processing for defective logical data blocksspecified by the INIT. In this case, alternate blocks are allocated in sparesectors in an alternate cell.− Auto alternate block allocation processingIf auto alternate block allocation processing is permitted by the AWREflag or the ARRE flag of the MODE SELECT parameters, the IDDexecutes alternate clock allocation automatically by alternate sectorprocessing for defective data blocks detected during execution of theWRITE, WRITE EXTENDED, WRITE AND VERIFY, READ andREAD EXTENDED commands. The alternate block allocation methodin this case is the same as in the case of the REASSIGN BLOCKScommand. See the description in Section 5.3.2 concerning "AutoAlternate Block Allocation Processing".
