duration in milliseconds that the read head of a hard disk
moves a data block to another on a platter. As the number of trays and the speed
is high, the better the access time. It is independent of connection type (IDE, SATA
90s, the average access time was 13 ms, a current hard drive allows less than 8
ms. SSD drives, using flash memory, go up to 85 microseconds, almost 100 times
less than the current mechanical disks.