I would like to know what determines bus speed in a CPU. I know about bus width, that all makes sense, but since electrical pulses travel at light speed I don't understand why bus speed is measured rather than just light speed. What on the bus means the signals aren't sent at light speed?

Thanks in advance.

  • $\begingroup$ does this help: computer.howstuffworks.com/motherboard4.htm $\endgroup$
    – Effie
    Sep 15, 2021 at 11:50
  • 2
    $\begingroup$ from what i read, speed is related to the "length" of a single bit (on one of the channels). It is the time the signal has to stay the same for the receiver to receive it. So basically it says with what frequency you can put new symbols on the bus. It is more of a data rate than speed. For some reason it is that way with a lot of communication systems. $\endgroup$
    – Effie
    Sep 15, 2021 at 12:27
  • $\begingroup$ Signal bus means more than one possible source of signals, as opposed to point to point communication. Arbitration may take much more time than the inverse of the max. signal/data rate. $\endgroup$
    – greybeard
    Sep 16, 2021 at 4:38

1 Answer 1


"Bus speed" isn't the right technical term, since it is ambiguous. The speed of electric signal depends on the speed of the electromagnetic wave in that medium, and is not necessarily equal to the speed of light in vacuum.

The maximum information data rate, reported in Bits/Second, is the rate at which data can be transferred without loss of information. This rate depends on the noise level present in the channel/bus, and is given by Shannon's formula.


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