# difference between a bus and a trace?



## kaseli

So I'm studying to get my A+ certification and they say that 'traces' are the copper pathways that are etched into the motherboard which the electricity flows through.

And when I tried to find out what 'busses' physically look like, the only thing I could find was a Yahoo answer saying that they basically are traces, not particularly different from all the other traces on a motherboard.

So my question is, what then is the difference between a trace and a bus?


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## voyagerfan99

The bus connects components together like the CPU and the memory.


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## kaseli

voyagerfan99 said:


> The bus connects components together like the CPU and the memory.



Right.  This is what I've read.  But then does the bus refer simply to a single specific trace or a specific collection of traces?  Because the traces are what connect everything on the motherboard, yes?

Or are busses not traces?  If not, what do they look like?


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## voyagerfan99

Have a look at this

http://www.wisegeek.com/what-is-a-motherboard-bus.htm


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## kaseli

voyagerfan99 said:


> Have a look at this
> 
> http://www.wisegeek.com/what-is-a-motherboard-bus.htm



Sorry, that didn't really help and kind of just made me more confused.

But I did some more google searching and I think I'm just going to stick with the idea that traces are a more general term than busses, and that busses are something like specific traces.

http://books.google.com/books?id=GZ...onepage&q=what are motherboard traces&f=false

"In Chapter One, PC Basics, I talked about the five primary busses of the computer system.  *These traces are the physical implementation of those busses on the motherboard.*"


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## tremmor

Its the etching on the boards. then they install the sockets, resistors and chips. its just a board. You can go into a radioshack store if available. they sell the boards and traces or and techniques for doing so.

heres and example of what im talking about.
http://en.wikipedia.org/wiki/File:S111FlipChipBack.jpg


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## beers

A trace is physical.
A bus is logical.

If you referenced something like the 'Front Side Bus' which would be more applicable to legacy type systems, you would use a variety of traces on the MB but the signaling/capacity on top of it would be your 'bus'.


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## kaseli

beers said:


> A trace is physical.
> A bus is logical.
> 
> If you referenced something like the 'Front Side Bus' which would be more applicable to legacy type systems, you would use a variety of traces on the MB but the signaling/capacity on top of it would be your 'bus'.



I'm sorry, I'm just really not understanding this.  Everything I've read seems to say that a bus is a physical connection.  What do you mean by 'a bus is logical'?

And I don't know what you mean by the 'signaling/capacity on top of it'


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## TrainTrackHack

Trace (as you know) is just the material on the board through which conducts electricity. Bus is a collection of physical connections, in addition to specifying how it works, i.e. a bus might be 64-bit, and transmit on both rising and falling edges of the clock signal. Or it might be 8-bit and use strobe instead of clock for syncing communications. Bus is logical in that these properties are independent of the existence of traces; you could built a 64-bit DDR bus or a 8-bit strobe bus out of wire or even pipes with water in them if you wanted to (although from engineering point of view neither is practical of course); even though "bus" generally implies the type of physical connection, the two can be separate.

Or, perhaps a poor analogy, but here goes: "trace" is like a piece of conducting wire (come to think of it, that's exactly what it is). All it is good for is transmitting electricity. The wire doesn't care what kind of electricity it transmits or what it's for; it might connect a battery to a device, it might be used to transmit Morse code using 1-, 5- or 12-volt DC (the revolutionary Morse bus specifies the lengths of tones and clicks as well as the voltages that may be used, but doesn't care how the sender and receiver are connected), or it might carry the data signal of USB. Perhaps I should use USB as an example: USB is a bus, and specifies the voltages used and how data is transmitted using the cable. A USB cable is, in a way, a "trace": it really doesn't care what kind of electricity goes through it, it simply sits there allowing current to flow between the devices so that they can communicate.


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## StrangleHold

Here is a simple way. Say your taking a trip/vacation=(Bus). Getting your stuff together, getting in the car, stopping for gas/food. getting to your destination. Having a good time and coming home. That's the bus. The road you drove on is the trace. What you did is a Bus as a whole.


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## kaseli

hackapelite said:


> Trace (as you know) is just the material on the board through which conducts electricity. Bus is a collection of physical connections, in addition to specifying how it works, i.e. a bus might be 64-bit, and transmit on both rising and falling edges of the clock signal. Or it might be 8-bit and use strobe instead of clock for syncing communications. Bus is logical in that these properties are independent of the existence of traces; you could built a 64-bit DDR bus or a 8-bit strobe bus out of wire or even pipes with water in them if you wanted to (although from engineering point of view neither is practical of course); even though "bus" generally implies the type of physical connection, the two can be separate.
> 
> Or, perhaps a poor analogy, but here goes: "trace" is like a piece of conducting wire (come to think of it, that's exactly what it is). All it is good for is transmitting electricity. The wire doesn't care what kind of electricity it transmits or what it's for; it might connect a battery to a device, it might be used to transmit Morse code using 1-, 5- or 12-volt DC (the revolutionary Morse bus specifies the lengths of tones and clicks as well as the voltages that may be used, but doesn't care how the sender and receiver are connected), or it might carry the data signal of USB. Perhaps I should use USB as an example: USB is a bus, and specifies the voltages used and how data is transmitted using the cable. A USB cable is, in a way, a "trace": it really doesn't care what kind of electricity goes through it, it simply sits there allowing current to flow between the devices so that they can communicate.



This helped a lot, thank you.


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