[robespierre]

A hard disk's transfer speed is determined by track capacity * rotation speed. For example, a disk with 54 sectors per track has 27,648 formatted bytes per track. If that disk spins at 3600 rpm or 60 1/s, its transfer speed from the HDA to the disk's SCSI processor is (27648 * 60) = 1,658,880 bytes/sec. Sequential reads will approach that speed, minus overhead.

Another example: The Quantum Atlas XP 32150 is a 7200 rpm, 2.1 GB drive with between 80–134 sectors per track. Using the same formula, its internal transfer speed is between (80 * 512 * 120) = 4,915,200 bytes/sec, and (134 * 512 * 120) = 8,232,960 bytes/sec. The highest sectors/track are on the outer cylinders at the logical beginning of the disk, which is why swap partitions should be located there for best performance. This model disk was sold with fast-wide 20 MB/s SCSI interface.