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Head Switch Time

Each cylinder contains a number of tracks, each accessible by one of the heads on the drive. To improve efficiency, the drive will normally use all of the tracks in a cylinder when doing a sequential read or write, because this saves the time required to physically move the heads to a new cylinder. Switching between heads is a purely electronic process instead of a mechanical one. However, switching between heads within a cylinder still requires a certain amount of time, called the head switch time. This is usually less than the track switch time.

The head switch time of the drive is often not specified. It is, compared to the other performance metrics, of somewhat less significance, but it should be realized that a drive with multiple platters doing a large block read or write will switch between heads much more often than it will switch between tracks.

Next: Track Switch Time

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