Difference between Seek Time and Disk Access Time in Disk Scheduling

Seek Time

The time taken for the hard disk controller to detect a specific piece of recorded data is known as the seek time. The amount of time it takes to find the head depends on where it is when the read/write request is issued. The read/write head of a disc drive moves to the correct place when something is read or written to it. Seeking refers to the physical location of the read/write head on the disk. Discovery time is the time it takes for a disk's read/write head to move from one disk to another. Due to the varying distance between the start point and where the read/write vertex is directed to travel, the search time for a particular disk may vary. As a result, seek time is usually expressed as average search time. Track to track and entire stroke are two more methods to quantify seek time.

• The read/write time taken to search or search between neighboring tracks is called track to track. It is measured in milliseconds (ms), which ranges from 2 to 4 ms but can be as short as 1 ms.
• The time taken to search the entire disk is called full stroke. A full stroke is also measured in milliseconds, and a search time of less than 10ms for hard disks is generally considered sufficient.

The operating system instructs the drive controller firmware to get data from a hard disc, which causes the read/write head to travel to the location where the data is stored. Switching between tracks necessitates the head actuator moving the access arm, which takes some time. This period is known as the discovery time. This varies depending on the distance between the tracks and the distance from its origin at the time of each read/write instruction.

Disk Access Time

The overall time taken by the computer to perform a read/write request and then obtain the relevant data from disc storage is known as disc access time. Disk access time is divided into two parts. The search time, which is when the read and write branch searches the required track, is the first component. Latency, or wait time, is the time it takes for the head write arm to wait for the required sector on the track to rotate around. The time it takes to access data on drives is measured in milliseconds. This is, however, far slower than the processing rates of CPUs. Although I/O is still sluggish, it cannot keep up with the advances in CPU performance.

There are two elements to disk access time:

• Data Transfer Time
• Access Time

Data Transfer Time

The time taken to transmit data between the system and the disk is known as the data transfer time. There are two types of data transfer time:

• Internal Transfer Rate: This is the time it takes for data to go from the disc surface to the hard disc cache.
• The time it takes to transport data between the hard disc cache and the system is known as the external transfer rate.

Access Time

The preparation time before the actual data transfer is denoted as Access Time. The read/write head, for example, is on track 1, but we need to read data from a different track or segment. As a result, before the actual transfer, the read/write head will relocate to the data block position. This lag is referred to as Access Time.

Differences

S no.	Seek Time	Disk Time
1.	The time it takes for the head to travel from the current track to the one with data is known as seek time.	The time it takes for a computer to perform a read/write request and obtain the data it needs is known as disc access time.
2.	Because seek time is a subset of disc access time, it is always smaller than disc access time.	When compared to Seek time, disc access time is relatively long.
3.	A data transmission is not taken into account while calculating seek time.	The time it takes to transmit data from one disc to another is referred to as disc access time.
4.	The amount of time it takes to seek varies greatly based on the distance between the present and ultimate positions and how it is ordered to proceed.	The two components of disc access time are access time and data transfer time.
5.	Depending on the RPS and drive grade, the seek time is normally between 10 and 20 milliseconds.	If we can cut access time and data transfer time, we can reduce disc access time.
6.	Average Seek Time is a metric for determining how long it takes to find something.	Seek time plus rotational latency plus data transfer time equals disc access time.