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1.8
Data Block Addressing
1.8.1
Definition of Data Space
The IDD manages the data storage area on the disk drive in the following 2 types of data
space.
•
User Space: User Data Storage Area
•
System Space: IDD Exclusive Area
Of these 2 areas the user can clearly access the user space. The data format and defect
management methods in this space are the same and it is possible to access this space by
logical data block addressing described in item 1.8.2. System space is accessed by the IDD
internally when the power is switched on or during processing of specific commands, but it
cannot be accessed directly by the user.
Fig. 1.4 shows the data space configuration on the disk drive. The number of cylinders
allocated to user space can be specified by the user (MODE SELECT or MODE SELECT
EXTENDED command).
A spare sector area (alternate area) for use as alternates for defective sectors is secured in user
space. The user can allocate the number of sectors in the final track of each cylinder and the
number of cylinders in the user space (alternate use cylinders) as alternate area (by the MODE
SELECT or MODE SELECT EXTENDED command).
Alternate data blocks are allocated in defect sector units for defective sectors on the disk media
through internal IDD defect management. Through this defect management, the INIT can
access all the logical data blocks in the user space as if they were error free.
For details concerning the data format on the disk media (cylinder configuration, track format
and sector format) and details concerning defect management techniques and alternate block
allocation techniques, Chapter 3 “Data Format” in the “Product Manual.” For an outline of
defect management techniques, see “Disk Media Management Techniques” in Chapter 5 of
this manual.