Unformatted text preview: ead just misses the target sector, and waits for the disk to make a full rotation. So the maximum rotational latency in seconds is: Ì
The average rotational latency, Ì
Ú Ñ Ü ÖÓØ Ø ÓÒ ÖÓØ Ø ÓÒ , is simply half of ÌÑ secs ¢ 60 min RPM 1
Ü ÖÓØ Ø ÓÒ . ¯ Transfer time: When the ﬁrst bit of the target sector is under the head, the drive can begin to read or write the contents of the sector. The transfer time for one sector depends on the rotational speed and the number of sectors per track. Thus, we can roughly estimate the average transfer time for one sector in seconds as: ½ ½ secs Ì Ú ØÖ Ò× Ö ¢ ¢ 60 min RPM ´average # sectors/track µ 1 We can estimate the average time to access a the contents of a disk sector as the sum of the average seek time, the average rotational latency, and the average transfer time. For example, consider a disk with the following parameters:
Parameter Rotational rate
Ì Ú× Average # sectors/track Value 7,200 RPM 9 ms 400 For this disk, the average rotational latency (in...
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