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C141-E034-02EN6 - 12
(2) Alternate cylinder assignment
A defective sector is assigned to the spare sector in the alternate cylinder.
This processing is performed when the automatic alternate processing is performed.
Figure 6.8 shows an example where (physical) sector 5 is detective on head 0 in cylinder 0.
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Index
Cylinder 0
Head 0
Head 0
Already
assigned
Defective
sector
4 alternate cylinders are provided for each head in zone 14 (inner side).
When an access request to sector 5 is specified, the device accesses the alternated sector in the
alternate cylinder instead of sector 5. When an access request to sectors next to sector 5 is
specified, the device seeks to cylinder 0, head 0, and continues the processing.
Defective sector is assigned to unassigned sector.
(unused)
Sector (logical)
Sector (physical)
Alternate
cylinder
214367
249248
Figure 6.8 Alternate cylinder assignment