Harddrive cache is a relative small cache on a hard drive.

Harddrive cache is a relative small cache on a hard drive.

This allows the drive to communicate at full interface speed while writing at slower of more opportune moment to the platters.

Example with queues: 1) Please write item A (somewhere on the outer tracks. 2) Please write item B (somewhere on the INNER tracks. 3) Please write item C (somewhere on the outer tracks.

Having a cache allows the drive to accept all three commands, but internally change the write order so both outer track writes are done sequentially.

A typical HDD cache from 2015 is about 64MB.