Shortest seek first (or shortest seek time first) is a

secondary storage Computer data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers. The central processing unit (CPU) of a computer ...

scheduling A schedule or a timetable, as a basic time-management tool, consists of a list of times at which possible task (project management), tasks, events, or actions are intended to take place, or of a sequence of events in the chronological order ...

algorithm to determine the motion of the

disk read-and-write head A disk read-and-write head is the small part of a disk drive which moves above the disk platter and transforms the platter's magnetic field into electrical current (reads the disk) or, vice versa, transforms electrical current into magnetic fi ...

in servicing read and write requests.

Description

This is a direct improvement upon a

first-come first-served Queueing theory is the mathematical study of waiting lines, or queues. A queueing model is constructed so that queue lengths and waiting time can be predicted. Queueing theory is generally considered a branch of operations research because the ...

(FCFS) algorithm. The drive maintains an incoming buffer of requests, and tied with each request is a cylinder number of the request. Lower cylinder numbers indicate that the cylinder is closer to the spindle, while higher numbers indicate the cylinder is farther away. The shortest seek first algorithm determines which request is closest to the current position of the head, and then services that request next.

Analysis

The shortest seek first algorithm has the direct benefit of simplicity and is clearly advantageous in comparison to the FIFO method, in that overall arm movement is reduced, resulting in a lower average response time. However, since the buffer is always getting new requests, these can skew the service time of requests that may be farthest away from the disk head's current location, if the new requests are all close to the current location; in fact,

starvation Starvation is a severe deficiency in caloric energy intake, below the level needed to maintain an organism's life. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, dea ...

may result, with the faraway requests never being able to make progress. The

elevator algorithm The elevator algorithm (also SCAN) is a hard disk, disk-I/O scheduling, scheduling algorithm to determine the motion of the disk's arm and head in servicing read and write requests. This algorithm is named after the behavior of a building elevat ...

is one alternative for reducing arm movement and response time, and ensuring consistent servicing of requests.

References

Disk scheduling algorithms {{compu-stub