In accessing a disk block the longest delay is due to A. Rotation time B. Seek time C. Transfer time D. Access time

The longest delay in accessing a disk block is typically due to the Seek Time.

Here's why:

A. Rotation Time: This is the time it takes for the desired sector of a disk to rotate into position under the read/write head. It's usually quite fast.

B. Seek Time: This is the time it takes for the read/write head to move to the desired track. If the data is spread out over the disk, the read/write head has to move quite a bit, which can take a significant amount of time. This is typically the longest delay.

C. Transfer Time: This is the time it takes to actually transfer the data. It's usually quite fast, especially compared to the seek time.

D. Access Time: This is a general term that refers to the time from when a request for data is made until the data is available. It includes the seek time, rotation time, and transfer time. So while it might be long, it's not a single factor like seek time.