The hard disk can execute such commands (for example, reading, writing and so) and then sends data and results back to the host, through this device again.
To communicate between the hard disk and the host (the computer) a special device is required to 'translate' USB commands to standard ATA commands. There is an IDE or S-ATA hard disk inside the external USB enclosures. It is hard to decide which is better and which is best to avoid. Many different USB (or firewire) external hard disks are available. Compatible USB hard disks, USB hard disk enclosures
