How do you calculate access time on a magnetic disk? Explain with the help of a suitable example.
Execution of a magnetic disk operation involves:
Wait time: The process waits to be granted device access.
Wait for device: Time the request spend in wait queue.
Wait for channel: Time until a shared 1/0 channel is available.
Positioning time: Time hardware need to position the head. Sometimes called the random access time: Consists of the time to move the disk arm to the desired cylinder, called the seek time Ts (in milliseconds), The time for the desired sector to rotate to the disk head, called the rotational latency (in milliseconds). Rotational speed, r, of 5000 to 10000 rpm.
Transfer rate is the rate at which data flow between the drive and the computer (megabytes of data per second). Transfer time: to transfer b bytes, with N bytes per track,