# Frequencies of CPU and bus

Discussion in 'Computing and Networks' started by wmzon, Jan 30, 2007.

1. ### wmzon Thread Starter New Member

Jan 30, 2007
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0
As far as I know computers operate on DC signals, which have no frequency, but the CPU and the bus are always classified in terms of frequency in megahertz or gigahertz. I have made a few inquiries to teachers, fellow students and friends but no one has been able to adequately explain this to me. Could any of you?

2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Hi,

Logic gates do output DC voltages. But nothing much happens if they just sit there in the same state. Transferring data on the bus between the processor and memory is under control of a signal - Read/^Write ( read as Read/Write-not, meaning that memory is read when Read is asserted HIGH, and is written to then The same signal is LOW). Older PC's had bus clocks running at 66 MHz, now they are up to 800 MHz. The main frequency associated with processors is a synchronizing clock signal that lets the processor execute instructions.

This is hardly a complete explanation of the operating frequencies to be found in a moder computer. You might want to go through Volume IV of the E-bbok on this site for a more complete explanation.

3. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
Sad to say the teachers, fellow students, and friends of whom you speak are so crushingly clueless.

4. ### Dave Retired Moderator

Nov 17, 2003
6,960
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CPUs are essentially sequential devices where data through put is processed in a sequential manner - consider the analogy of something flowing down a pipeline. Therefore, requires some form of control signal (the clock signal) which clocks the data through the CPU pipeline - this what is classified as clock frequency you talk of, i.e. MHz/GHz.

Computers do not operate on DC signals perse, though digital logic requires one of two binary states: '0' and '1' - which is achieved through two different voltage levels, which I suppose induces the impression that computers operate on DC signals. See Volume IV - Chapter 3.1. The fact is the gates will be able to represented one of two states (dictated by the gate rails) though the act of threading the data through the gate is an analogue task. I can understand your peers not understanding this, but if your teacher doesn't know then I would be very worried!

Dave