Conventional universal serial bus (USB) flash drives are NAND-type flash memory data storage devices integrated with a USB interface. Conventional USB flash drives are typically small, lightweight, removable and rewritable. These USB flash drives are commonly known as “thumb drives” and “data sticks.”
USB flash drives have several advantages over other portable storage devices, particularly the floppy disk. Conventional USB flash drives are generally faster, hold more data, and are considered more reliable (due to their lack of moving parts) than floppy disks. Conventional USB flash drives use the USB mass storage standard, supported natively by modern operating systems such as Linux, Mac OS X, and Windows XP.
Conventional USB flash drives include a small printed circuit board encased in a robust plastic or metal casing, making the drive sturdy enough to be carried about in a pocket, as a key fob, or on a lanyard. Only a USB interface protrudes from this protection, and is usually covered by a removable cap. Most conventional USB flash drives use a standard type-A USB connection allowing them to be connected directly to a port on a personal computer. USB interfaces are also known as USB connectors.
Most conventional USB flash drives are active only when powered by a USB computer connection, and require no other external power source or battery power source; conventional USB flash drives are powered using the limited supply afforded by the USB connection. To access the data stored in a flash drive, the conventional USB flash drives must be connected to a computer, either by direct connection to the computer's USB port or via a USB hub. USB drives are quickly replacing CD ROMs, floppy drives, and even printed matter in usage.
One end of conventional USB flash drives is fitted with a single male type-A USB interface. Inside the plastic casing is a small printed circuit board. Mounted on this board are simple power circuitry and a small number of surface-mounted integrated circuits (ICs). Typically, one of these ICs provides an interface to the USB port, another drives the onboard memory, and yet another is the flash memory.
The essential components of conventional USB flash drives are a male type-A USB interface, a USB mass storage controller, a NAND flash memory chip and a crystal oscillator. The male type-A USB interface provides an interface to the host computer. The USB mass storage controller includes a USB host controller and provides a linear interface to block-oriented serial flash devices while hiding the complexities of block-orientation, block erasure, and wear balancing or wear leveling. The USB mass storage controller contains a small RISC microprocessor and a small amount of on-chip ROM and RAM. The NAND flash memory chip stores data. The crystal oscillator produces a 12 MHz clock signal and controls data output through a phase-locked loop.
Often the amount of data storage capacity that is available to a personal computer on a USB flash drive is less than the amount of data storage capacity on the USB flash drive that is useful to the computer. By definition, USB flash drives are limited in the amount of data that can be stored thereon because the NAND flash memory chip is manufactured with a certain amount of data storage capacity. The data storage capacity can be increased by physically replacing the NAND flash memory chip, but physically replacing the NAND flash memory chip costs many more times the price of the original USB flash drive, and accordingly, replacing the NAND flash memory chip is not performed except under the most extraordinary of circumstances.
Another option to increase the amount of data storage capacity that is available to a personal computer on a USB flash drive is to connect multiple USB flash drives to multiple USB ports on the computer. However, the number of USB ports that is available on a computer is usually limited to 2 or 3 USB ports, so the number of USB flash drives that can be connected is 2 or 3. Each of the USB flash drives is identified and accessible to the computer as a unique external drive, each having a unique drive identification, such as “D”, “E”, “F” and so forth. However, each of the USB flash drives having a unique and different drive identification increases the complexity of locating data on the USB flash drives.
Another conventional way to increase the amount of data storage capacity that is available to a personal computer on a USB flash drive is to connect multiple USB flash drives through one of more USB hubs that are in turn connected to the computer. However, this technique still has the problem that each drive has a unique and different drive identification, which in turn increases the complexity of locating data on the USB flash drives. This technique is also ultimately limited by the number of USB ports on the computer and the number of USB devices that can be connected to each port.
There is a need in the art to increase the storage capacity that is available to a personal computer on a USB flash drive. There is also a need in the art to reduce the complexity of locating data on multiple USB flash drives connected to a computer.