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A keydrive (also USB key, USB flash drive, keychain drive) is a small data storage device that uses flash memory to store information without the need for batteries. Keydrives are also impervious to the scratches and dust that have plagued previous forms of portable storage media like Compact Discs and floppy disks.

Most modern operating systems can read and write to keydrives without any special device drivers. Microsoft's Windows Me, 2000 and XP are able to access them, but Windows 98, which was one of the first OSes with much support for USB, needs specialized software for each different type of USB storage device it encounters. MS-DOS doesn´t include support for USB ( nor for USB booting).

As of 2003, most keydrives in existence ran at the USB 1.0/1.1 speeds of 1.5 Mbit/s or 12 Mbit/s. However, newer USB keys had the capability to utilize the high-speed USB 2.0, which tops out at 480 Mbit/s. They have ranged from a few megabytes in size up to a few gigabytes, although some computers have trouble reading and writing to devices that have more than 2 GB of storage.

Most USB flash drives are small and lightweight. Some are light enough that they could hypothetically be carried by 14 ants. They are popular with people who need to carry data between home and school or work. Theoretically, the flash memory in the drives can retain data for 10 years.

Some computers have the ability to boot up from keydrives, but that capability must be supported in the computer's BIOS.

See also : BIOS boot devices, including USB.

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