LOOK is a disk scheduling

I/O scheduling

Input/output scheduling is a term used to describe the method computer operating systems decide the order that block I/O operations will be submitted to storage volumes...

 algorithm used to determine the order in which new disk read and write requests are processed.

Description

LOOK is similar to SCAN

Elevator algorithm

The elevator algorithm is a disk scheduling algorithm to determine the motion of the disk's arm and head in servicing read and write requests....

 in that the heads sweep across the disk surface in both directions performing reads and writes. However, unlike SCAN, which visits the innermost and outermost cylinders each sweep, LOOK will change directions when it has reached the last request in the current direction.

Variants

One variant of LOOK is C-LOOK, which fulfills requests in one direction only. That is, C-LOOK starts at the innermost cylinder requested and moves outward fulfilling requests until it reaches the last request. Then it moves directly back to the innermost request and starts fulfilling requests moving outward again.

Performance

LOOK has slightly better average seek times than SCAN. C-LOOK has a slightly lower variance in seek time than LOOK since the worst case seek time is nearly cut in half.

See also

Other variations include:

• SCAN
  Elevator algorithm
  The elevator algorithm is a disk scheduling algorithm to determine the motion of the disk's arm and head in servicing read and write requests....
  
   - Elevator algorithm
• FSCAN
  FSCAN
  FScan is a disk scheduling algorithm to determine the motion of the disk's arm and head in servicing read and write requests.It uses two subqueues. During the scan, all of the requests are in the first queue and all new requests are put into the second queue. Thus, service of new requests is...
  
  
• N-Step-SCAN
  N-Step-SCAN
  N-Step-SCAN is a disk scheduling algorithm to determine the motion of the disk's arm and head in servicing read and write requests....