Capacity - Usable Vs Stated
When you purchase any hard drive, it must be understood that the stated capacity of the disk is that of an unformatted drive. In order for the disk drive to become usable, it needs to be prepared in a format readable by your computer's operating system.
Unformatted Disk Capacities
It is the formatting that allows data to be stored and retrieved, once stored. However, this process uses a certain amount of disk space, known as `overhead'. The reason why disk capacities are not stated showing their formatted capacity is that different operating systems and applications may use more or less disk space for formatting.
Usable Disk Space
Our external drives are sent out in a FAT 32 format, which is compatible with Windows and Mac based computers, using roughly 7% of disk space. Therefore, on an average 250GB hard drive almost 18Gbs of disk space are sacrificed for the purpose of formatting so that the usable space you are left with is 232GB.