sector interleave


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sector interleave

[′sek·tər ′in·tər‚lēv]
(computer science)
A sequence indicating the order in which sectors are arranged on a hard disk, generally so as to minimize access times. Also known as sector map.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

sector interleave

(Or sector map) The mapping from logical to physical sector numbers on a magnetic disk designed to optimise sequential reads and writes. Data is usually transferred to and from the disk in blocks or sectors where one sector lies within a continuous range of rotational angle of the disk. If logical sectors are assigned sequentially to physical sectors (0,1,2,...) then by the time one sector has been read and processed (e.g. writen to main memory) the start of the next logical sector will have passed the read/write head and will not be accessible until the disk's rotation brings it back under the head.

Staggering the physical sectors (e.g. 0,3,6,1,4,7,2,5,8) aims to allow just enough time deal with one sector before the next is accessible. This obviously depends on the relative speed of the rotation of the disk, sector size, sectors per track and the speed of transfer of sectors to main memory.
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sector interleave

The way sectors are numbered on a hard disk. Created with a low-level format, the optimum interleave is determined by the speed of the drive. In a 1:1 interleave, sectors are one after the other (0,1,2,3, etc.). A 2:1 interleave alternates them (0,4,1,5,2,6,3,7).

With a 1:1 interleave, the disk controller must be fast enough to read sector 2 after it reads sector 1, otherwise the beginning of sector 2 will pass by the read/write head and require a full rotation to come under the head again. A 2:1 or 3:1 interleave provides more time to read sequential sectors in one rotation. See sector.
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