What are seek time and rotational latency?

What are seek time and rotational latency?

Seek time – The time taken by the R-W head to reach the desired track from it’s current position. Rotational latency – Time taken by the sector to come under the R-W head. Data transfer time – Time taken to transfer the required amount of data. It depends upon the rotational speed.

How do you calculate rotational latency?

Thus, on average, the rotational latency is half the time it takes the disk to make a complete revolution. The disk spins at 10000 RPM, so it takes 1/10000 of a minute to make one revolution. Equivalently, (1000 ms/sec × 60 sec/minute) / 10000 RPM = 6 ms to make one revolution. So rotational latency is 3ms.

What is rotational latency time?

Rotational latency (sometimes called rotational delay or just latency) is the delay waiting for the rotation of the disk to bring the required disk sector under the read-write head. It depends on the rotational speed of a disk (or spindle motor), measured in revolutions per minute (RPM).

What do you mean by seek time and latency time?

Seek time is the time taken for a hard disk controller to locate a specific piece of stored data. Other delays include transfer time (data rate) and rotational delay (latency). The amount of time that it takes the read/write head of the disc to to move from on part fo the disk to another is called the seek time.

Why is rotational latency usually not considered?

Most disk scheduling do not consider rotational frequency because in most modern system, the actual physical location of blocks in not available. It can be reduced if subsequent request belongs to same track or near. It can be reduced if subsequent request belongs to adjacent sector.

What is the maximum rotational latency?

Difference between Rotational Latency and Transfer Time in Disk Scheduling :

Rotational Latency Time Transfer Time
Maximum latency = 60/rpm Average latency = 0.5*Latency Time It takes about 1 sec to transfer 30-60MB of data

What is the average time to read a single sector?

Best Answer Average is half that, or 8.3 ms. Transfer time: 512 / 3.5 MB/s = 146 µs — however, it will take a little longer to actually read the sector, since there are 64 sectors on the disk, and the disk rotates once every 16.7 ms, each sector will take 16.7 ms / 64 = 260 µs to read.

What is the difference between seek time and latency?

A disk is divided into many circular tracks. Seek Time is defined as the time required by the read/write head to move from one track to another….Difference between Seek Time and Rotational Latency in Disk Scheduling.

S.NO. Seek Time Rotational Latency
3 It can be reduced if subsequent request belongs to same track or near. It can be reduced if subsequent request belongs to adjacent sector.

Is there any way to implement truly stable storage?

10.6 Is there any way to implement truly stable storage? Explain your answer. Answer: The fundamental technique for stable storage is to maintain multiple copies of the data, so that if one copy is destroyed, some other copy is still available for use.

What is rotational latency WRT disk scheduling?

Rotational Latency: Rotational Latency is the time taken by the desired sector of disk to rotate into a position so that it can access the read/write heads. So the disk scheduling algorithm that gives minimum rotational latency is better.

What is the difference between rotational latency and seek time?

Rotational Latency: The disk is divided into many circular tracks, and these tracks are further divided into blocks knows as sectors. The time required by the read/write head to rotate to the requested sector from the current position is called Rotational Latency.

What is the average latency of a disk?

The average rotational latency for a disk is one-half the amount of time it takes for the disk to make one revolution. Seek time is the amount of time it take for the ReadWrite head to move between sectors on the disk. Some times data needs to be written on the outside of the platters and sometimes inside.

How is rotational latency measured in a platter?

The time taken by the platter to rotate and position the data under the R/W head is called rotational latency. This latency depends on the rotation speed of the spindle and is measured in milliseconds. The average rotational latency is one-half of the time taken for a full rotation.

How is the seek time of a rotating disk drive determined?

A rotating drive’s average seek time is the average of all possible seek times which technically is the time to do all possible seeks divided by the number of all possible seeks, but in practice it is determined by statistical methods or simply approximated as the time of a seek over one-third of the number of tracks.