A computer flash drive is a small, portable flash memory card that plugs into a computer’s USB port and functions as a portable hard drive. Computer flash drives are touted as being easy-to-use as they are small enough to be carried in a pocket and can plug into any computer with a USB drive. Generally computer flash drives have less storage capacity than an external hard drive, but they are smaller and more durable because they do not contain any internal moving parts. A flash drive is not a component built into any computer .A flash drive is a portable storage device that allows you to copy/save information on to it and take it with you wherever you go. This way you can access the information on it from any computer with a USB port. A USB thumb drive is a type of data storage devices that includes flash memory with an integrated USB interface. USB pen drives are typically removable and rewritable, and physically much smaller than a floppy disk. USB flash disks often used for the same purposes for which floppy disks or CD-ROMs were used earlier. They are smaller, faster, have thousands of times more capacity, and are more durable and reliable because they have no moving parts. Until some years ago, most desktop and laptop computers were supplied with floppy disk drives, but floppy disk drives have been abandoned in favour of USB 2.0 or more recently with USB 3.0 ports. Computer flash drive draws power from the computer through the USB connection. When the user plugs the device into the USB 2.0 or 3.0ports, the computer's operating system recognizes the device as a removable drive and assigns it a drive letter. Compared to hard drives, usb flash drives use little power, have no fragile moving parts, and for most capacities are small and light. Data stored on flash drives is impervious to mechanical shock, magnetic fields, scratches and dust. These properties make them suitable for transporting data from place to place and keeping the data readily at hand. Computer Flash drives also store data densely compared to many removable media. Flash drives implement the USB mass storage device class so that most modern operating systems can read and write to them without installing device drivers. Some computers can boot up from flash drives. Specially manufactured usb flash drives are available that have a tough rubber or metal casing designed to be waterproof and virtually "unbreakable". Like all flash memory devices, computer flash drives can sustain only a limited number of write and erase cycles before the drive fails. This should be a consideration when using a computer flash drive to run application software or an operating system. Most USB flash drives no longer include a write-protect mechanism, although a small number have a switch on the housing of the drive itself to keep the host computer from writing or modifying data on the drive. A drawback to the small size of flash drives is that they are easily misplaced, left behind, or otherwise lost. This is a particular problem if the data they contain are sensitive. As a consequence, some manufacturers have added encryption hardware to their drives.