The following information is from the website: http://en.wikipedia.org/wiki/External_hard_disk_drive
An external hard disk drive is a type of hard disk drive which is connected to a computer by a USB cable or other means. Modern entries into the market consist of standard SATA, IDE, or SCSI hard drives in portable disk enclosures with SCSI, USB, IEEE 1394 Firewire, eSATA client interfaces to connect to the host computer.
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The external (portable) hard drive is like the thump drive but the size of the tool is bigger and heavier, and the storage capacity is larger than the thump drive. The external hard drive is durable more than the thump drive. The computer must have the internal hard drive. The external hard drive is the optional peripheral to the computer.
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