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I want a partition for storing temporary files (such as pagefile.sys on Windows, or linux swap partition), and I want this partition be faster than others.

We all know that the platter spin speed of the outer side of the platter is faster than the inner side. Almost all partition software use a bar chart to show partitions, thus I don't know how partitions are physically located on HDD platters. As a result I don't know which partition is faster.

Is the physical shape of a partition on the platter like a ring, or a piece of pie (as illustrator on this site )?

What about multiple platters cases? For example: paritioning a 2TB HDD which has 3 platters into 3 partitions with same size. Does each partition occupy a single platter, or does each partition consist of several rings/pies from each platter?

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1 Answer 1

up vote 2 down vote accepted

The purpose of having multiple platters is not only to go beyond the limitations of storage density, but also to increase throughput. The heads on a hard drive move together across all the platters (even on a single platter drive, there are two heads moving together on the top and bottom). This means when the heads are on a particular cylinder (the term used to refer to the tracks aligned at the same location across multiple sides and platters), the information from multiple platters can be read simultaneously and processed by the drive controller.

The performance of magnetic hard drives depend mainly on three factors:

  • Rotational latency (depends on the speed of rotation, like 5400rpm, 7200rpm, 10000rpm and so on)
  • Seek time (the average duration taken by the heads to move to a particular track)
  • Buffer memory (the higher the buffer, the better)

Considering the above factors, it makes sense that data is written across platters on a single cylinder first before moving on to the next cylinder so that the impact of seek time is minimized. Expanding this to partitions, the allocation should be ring shaped (covering several cylinders across platters) to maximize performance. This is how the addressing mechanism (LBA) works on hard drives.

The pie shaped schematic shown in the site you mentioned is not how it is allocated. Such an allocation would cause much poorer performance.

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I guess the LBA and CHS equivalence table in LBA CHS conversion section also shows the same result. When LBA address increasing, sector will increase first, then head, then cylinder. –  LiuYan 刘研 Oct 24 '12 at 16:57
Yes, that's why the explanation given in the answer is appropriate for the question. –  M K Oct 24 '12 at 17:37

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