Universal Serial Bus

hardware, standard (USB) An external peripheral interface

standard for communication between a computer and external

peripherals over an inexpensive cable using biserial

transmission.

USB is intended to replace existing serial ports, parallelports, keyboard, and monitor connectors and be used with

keyboards, mice, monitors, printers, and possibly some

low-speed scanners and removable hard drives. For faster

devices existing IDE, SCSI, or emerging FC-AL or

FireWire interfaces can be used.

USB works at 12 Mbps with specific consideration for low cost

peripherals. It supports up to 127 devices and both

isochronous and asynchronous data transfers. Cables can

be up to five metres long and it includes built-in power

distribution for low power devices. It supports daisychaining through a tiered star multidrop topology. A USB

cable has a rectangular "Type A" plug at the computer end and

a square "Type B" plug at the peripheral end.

Before March 1996 Intel started to integrate the necessary

logic into PC chip sets and encourage other manufacturers

to do likewise. It was widely available by 1997. Later

versions of Windows 95 included support for it. It was

standard on Macintosh computers in 1999.

USB 2.0 is a much faster enhanced version.

usb.org .

(2002-01-01)