sector interleave

Sector numbering on a hard disk. A one to one interleave (1:1) is sequential: 0,1,2,3, etc. A 2:1 interleave staggers sectors every other one: 0,4,1,5,2,6,3,7.

In 1:1, after data in sector 1 is read, the disk controller must be fast enough to read sector 2, otherwise the beginning of sector 2 will pass the read/write head and must rotate around to come under the head again. If it isn't fast enough, a 2:1 or 3:1 interleave gives it time to read all sectors in a single rotation, eliminating wasted rotations. The best interleave is based on the speed of the particular disk drive. Interleaves are created with the low-level format.

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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.