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.