Article 117 - Hard Drive RPM to IO Correlation

There are different types of hard drives. Consumers are most familiar with IDE, SATA, SATA2, and SATA3 hard drives but in truth these are only marketing schemes. The true value of the hard drive is most strongly affected by the rotations per minute (RPM).

Since most of the hard drive access is considered random, that is the disk head is repeatedly accessing non-adjacent sectors, the disk arm needs to move. By virtue of mechanical limitations, the disk arm and disk head can only do so much per second. There are other limitations as well such as maximum disk rotational speeds, which could affect integrity but that is beyond scope of this article. Though, it is worth while to note that disk rotation speeds are capped to prevent lost of data due to scratching of disk head and disk cylinder.

In modern hard drive specifications, there are predominantly three speeds of hard drive rated speeds, 5400RPM, 7200RPM, and 10000RPM; the last being the fastest of them all.

A 5400RPM hard drive can produce about 150 random IO operations per second.

A 7200RPM hard drive can produce about 225 random IO operations per second.

A 10000RPM hard drive can produce about 300 random IO operations per second.

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