sector interleave


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.

sector interleave

(Or sector map) The mapping from logical to physical sectornumbers on a magnetic disk designed to optimise sequentialreads and writes. Data is usually transferred to and from thedisk in blocks or sectors where one sector lies within acontinuous range of rotational angle of the disk. If logicalsectors are assigned sequentially to physical sectors(0,1,2,...) then by the time one sector has been read andprocessed (e.g. writen to main memory) the start of the nextlogical sector will have passed the read/write head and willnot be accessible until the disk's rotation brings it backunder the head.

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

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.