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Unformatted text preview: s the logical block number into a (surface, track, sector) triple that uniquely identiﬁes the corresponding physical sector. Hardware on the controller interprets this triple to move the heads to the appropriate cylinder, waits for the sector to pass under the head, gathers up the bits sensed by the head into a small buffer on the controller, and copies them into main memory.
Aside: Formatted disk capacity. Before a disk can be used to store data, it must be formatted by the disk controller. This involves ﬁlling in the gaps between sectors with information that identiﬁes the sectors, identifying any cylinders with surface defects and taking them out of action, and setting aside a set of cylinders in each zone as spares that can be called into action if one of more cylinders in the zone goes bad during the lifetime of the disk. The formatted capacity quoted by disk manufacturers is less than the maximum capacity because of the existence of these spare cylinders. End Aside. 290 CHAPTER 6. THE MEMORY HIERARCHY Accessing Disks
Devices such as...
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- Spring '10
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