What defines the time taken to position the sector on the platter under the read/write head?

Question

Options

• ARotational delay
• BSeek time
• CResponse time
• DData transfer rate

• A
  81% (30)
• B
  3% (1)
• C
  5% (2)
• D
  11% (4)

Explanation

Rotational Latency To access data, the actuator arm moves the R/W head over the platter to a particular track while the platter spins to position the requested sector under the R/W head. 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. Similar to the seek time, rotational latency has more impact on the reading/writing of random sectors on the disk than on the same operations on adjacent sectors. Average rotational latency is approximately 5.5 ms for a 5,400-rpm drive, and around 2.0 ms for a 15,000-rpm (or 250-rps revolution per second) drive as shown here. Av. rotational latency for 15K rpm or 250 rps (15000/60) drive is = (1/2)/250=2 milliseconds.

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