Electrically, a bus is a set of wires, which when taken in parallel, are used to transmit data. Typically, multiple devices are connected to a bus, in contrast to many other forms of interconnect, which merely connect one output to another input. See point to point. Because of this, there is often special logic to control who is allowed to write to the bus. See transfer gates, three state logic.
Some common busses associated with computers are SCSI, IDE, PCI, ISA.
BUS is also used as a three-letter acronym for Bodies Under Siege. BUS is both a book and a mailing list devoted to self-injury. I honestly haven't read the book, but it's received high praise for treating the subject as a legitimate concern and a sign of a larger problem, not just a cry for attention. The mailing list itself is mostly concerned with helping its members break the terrible cycles involved in hurting yourself.

Other books on the subject:

  • A Bright Red Scream : Self-Mutilation and the Language of Pain
  • Bodily Harm : The Breakthrough Healing Program for Self-Injurers
  • Cutting: Understanding and Overcoming Self-Mutilation

See also: http://www.palace.net/~llama/psych/busfaq.html

A bus, in computing terms, is a set of wires designed to transfers data, addresses and control information from a specified source to a specified destination. There are two main types of buses:

  • Internal buses – which connect the various registers and internal components of the CPU.
  • External buses – which connect the CPU to main memory and to the input/output units.

A bus may be unidirectional, capable of sending in one direction only, or it may be bi-directional. A dedicated bus is a unidirectional bus connecting one source and one destination.

For these reasons, a shared bus system is often used, even though simultaneous transfer of data is no longer possible. A further advantage of a shared bus system is that more devices can easily be added.

To Sum up shared and dedicated buses

  • Shared buses have all the devices on one bus – an example being the PCI bus.
  • Dedicated bus is to connect one specific device to another specific device – an example being the bus that connects the CPU with the main memory.

In addition there are control buses. Control buses are used to send control signals between the control unit and the ALU, between the processor and memory, and between processor units and peripherals. Examples of such signals are:

  • Signals to directly control the operation of the ALU
  • Signals to indicates a status condition such as ‘busy’ or ‘operation complete’
  • Signals to indicate that an error condition such as overflow has occurred.
  • Start and stop signals and timing information
Those little pathways that channel data and instructions between memory, registers and elements (or as jakohn said it, multiple devices).

The word bus is derived from the latin omnibus with the idea that several sets of chips can be connected to the same bus and share the same communication channels.

Three buses are usually within the processor, the data bus (for transferring data, duh), the address bus (for communications between the control unit and memory) and the control bus (for transmitting signals between components).
The use of "bus" for both a public transit system vehicle and a set of data transmission wires comes from the Latin word "omnibus," the dative plural of "omnes," or all. "Omnibus" was used as a name for transportation in France, starting in the city of Nantes in 1828. Some sources say that the public system was called a "voiture omnibus" (car for everyone) and others that it comes from a shopkeeper who punned on his own last name, Omnes, so that his store near the terminal of the horse-drawn vehicles was called "Omnes Omnibus" (Everything for Everyone) and the name was attached to the transportation.

In any case, the name "omnibus" stuck when England picked up the idea of the vehicles the next year. If the word had been French rather than Latin, a new name would probably have been given to the vehicles, but as it was, the word "omnibus" acquired a figurative use quite soon; in 1831 Washington Irving could say about the passage of reform legislation, "the Great Reform Omnibus moves slowly." After that, "omnibus" started to mean any kind of collection of dissimilar things.

The first shortening of omnibus to "bus" is recorded in 1832. The words tended to be used interchangeably for several decades, but by 1888 bus was also used as a verb for traveling by bus, while the longer form never became a verb. (In the latter half of the 20th century, of course, "busing" would became a controversial issue in the United States and be made a noun all over again.)

Pioneering electricians called a rod that carried all the power from a source an "omnibus bar," which became "bus bar," and just "bus" as early as 1930. This name carried over to early computers, so that in 1946, the Annals of the Computation Lab of Harvard University could say, "All units in the machine are connected to the central distribution buss over which numbers are transferred from one unit to another with the aid of timed electrical impulses." Despite the variable number of Ss in the word, its meaning remained essentially the same as computer technology expanded.

Sources:
Hibbert, Christopher. The English: A Social History 1066-1945. New York: W.W. Norton & Company, 1987.
http://dictionary.oed.com
http://www.britishbus.co.uk/horsebus.htm
http://www.quido.cz/objevy/autobus.a.htm
http://www.quinion.com/words/articles/omnibus.htm

Bus (?), n. [Abbreviated from omnibus.]

An omnibus.

[Colloq.]

 

© Webster 1913.

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