Universal Serial Bus
USB 2.0

    (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.

   <usb.org>.

   (2004-01-31)