What are the Magnetic disk and Flash drives
External Hard Drives: These includes devices located outside the main computer case. This drive allows the user to store information on a hard drive that is not inside the computer. The external hard drive is connected to the computer via a high-speed cable, usually with USB interface.
Dual Hard Drives: Having two hard drives in one computer works much the same way as a removable hard drive system. The drawbacks of this sort of scheme, however are more significant. First, it is not going to help much against theft, fire, sabotage, many types of viruses, and even some types of hardware failure. Second, you can only have a single backup, which makes the whole system very vulnerable--if you make a copy of the whole disk every night, what happens if you only notice a problem three days after it wipes out some of your data? Finally, the temptation is great to use the second drive for more data and discontinue the backup procedure when the first disk gets filled up.
RAID: RAID (Redundant Array of Inexpensive Disks) is a method of combining several hard drives into one unit. It can offer fault tolerance and higher throughput levels than a single hard drive or group of independent hard drives. RAID provides real-time data recovery when a hard drive fails, increasing system uptime and network availability while protecting against loss of data. Multiple drives working together also increase system performance.
A USB Flash drive consists of flash memory data storage device integrated with USB (Universal Serial Bus). Storage capacities can range from 64 MB to 256 GB. Some of them allow about 1 million write and erase cycles. They don't have moving parts - everything is electronic instead of mechanical. Flash memory drives comes in a variety forms. These drives are used for easy and fast information storage and exchange in computers, digital cameras and home video game consoles. For more information see: http://www.usbflashdrive.org/