Universal Serial Bus
(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, parallel ports, 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 daisy chaining 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.
The USB 2.0 specification was released in 2000 to allow USB to compete with Firewire etc. USB 2.0 is backward compatible with USB 1.1 but works at 480 Mbps.