Motivation
The original motivation for the Universal Serial Bus (USB) came from three interrelated considerations:
• Connection of the PC to the telephone
It is well understood that the merge of computing and communication will be the basis for the next
generation of productivity applications. The movement of machine-oriented and human-oriented data
types from one location or environment to another depends on ubiquitous and cheap connectivity.
Unfortunately, the computing and communication industries have evolved independently. The USB
provides a ubiquitous link that can be used across a wide range of PC-to-telephone interconnects.
• Ease-of-use
The lack of flexibility in reconfiguring the PC has been acknowledged as the Achilles’ heel to its
further deployment. The combination of user-friendly graphical interfaces and the hardware and
software mechanisms associated with new-generation bus architectures have made computers less
confrontational and easier to reconfigure. However, from the end user’s point of view, the PC’s I/O
interfaces, such as serial/parallel ports, keyboard/mouse/joystick interfaces, etc., do not have the
attributes of plug-and-play.
• Port expansion
The addition of external peripherals continues to be constrained by port availability. The lack of a bi-
directional, low-cost, low-to-mid speed peripheral bus has held back the creative proliferation of
peripherals such as telephone/fax/modem adapters, answering machines, scanners, PDA’s, keyboards,
mice, etc. Existing interconnects are optimized for one or two point products. As each new function or
capability is added to the PC, a new interface has been defined to address this need.
