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I have been studying buses used in communication systems. From what I read at Wikipedia,

"In computer architecture, a bus (from the Latin omnibus, meaning "for all") is a communication system that transfers data between components inside a computer, or between computers. This expression covers all related hardware components (wire, optical fiber, etc.) and software, including communication protocol."

Does that mean both a wire and a bus is the same thing? What feature makes the bus totally different from a normal wire in the first place?

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A house is a building, but a building isn't always a house. –  Scott Seidman Jan 11 at 23:11
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up vote 6 down vote accepted

A wire can be a bus if it is a serial link carrying many individual pieces of information. More usually, a bus is regarded as a collection of wires that transport digital information from A to B. 64 bit processors (PCs etc.) have a 64 bit-wide bus between the CPU and their memory chips and possibly to other devices.

It doesn't have to be inside a computer of course - anything that is transmitting information from A to B will use some form of wire or collection of wires for achieving those aims.

What differentiates a wire as not being a bus is that it only carries one coherent "entity" such as power or a microphone signal or is connected to an on/off switch or a guitar or a speaker. A bus is usually digital.

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May I ask where you get the idea that 64 bit processors (PCs etc.) have a 64 bit-wide bus between the CPU and their memory chips? All Intel processors that fit the LGA-2011 Socket have 256 data pins, connecting to 256 data lines on the motherboard that lead to the DRAM. The LGA-2011 Socket datasheet, section 6.1. –  davidcary Jan 12 at 1:52
    
@davidcary Andy was probably thinking of the address, but of course that isn't actually 64-bit either. But actually looking at that data sheet, the data bus to each DIMM is indeed 64 bits. –  derobert Jan 12 at 5:44
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I usually consider a bus a union of many wires. Imagine an address data bus with A15..A0 .. 16 wires, 1 bus. This is valid for very low level hardware.

Once you think about protocols, a bus is usually more a description of a topology type.

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I see a wire as a single signal, a buss is a collection of signals/wires. But there are single wire buses that use timing to convey more then one bit of info... –  dfowler7437 Jan 11 at 20:39
    
@dfowler7437: For reference, a "buss" is a kiss. :) –  cHao Jan 11 at 23:28
    
@cHao.. right! an extra s changes everything.. LOL –  dfowler7437 Jan 13 at 0:33
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One differentiating feature of a bus is that more than one device on a bus can send information. A device on a bus not only receives information; it can also reply. If it replies over some different wire(s) than the one(s) where it receives, then both (sets of) wires make up the bus.

If the information comes from a single source, and all the other devices are simply passive listeners with no way to reply, that's not a bus.

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