CPU's and System Buses??

[Beno]

Hi All,

Could any of you please give me some clear explanations to these questions. When we talk about processor speed, well the speed of the actual computer is not based upon the given processor speed but is based upon the speed of the system bus. So my question goes like this........... how does a processor work at the speed it does when it can only effectively work at the speed of the system bus. I know any processor wont work at its maximum speed because assembly instructions in programs 99% of the time take longer than 1 machine cycle to execute so therefore for example a 333Mhz processor like mine will probably actually run at around 300Mhz but how does it do this when my system bus speed is 66Mhz??

And when we refer to system bus........is this the bus that ALL computer components on the motherboard are connected to, or is it just the CPU and RAM??

And one more question.............what are the major differences between ISA and PCI buses.
I know PCI is the new common type of bus, but why is it better than ISA and is PCI being used as a system bus??

Thanks again everyone.....this is the best discussion board I have ever come across.

Cheers

Ben
http://www.PCGuide.com/ubb/cool.gif

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Have a nice day

[Paleo Pete]

System Buses (http://www.pcguide.com/ref/mbsys/buses/index.htm) is a very good article, with explanations of the different buses used in the computer. This article deals with local buses, such as ISA, VLB and PCI.

External Processor Interfaces (http://www.pcguide.com/ref/cpu/arch/ext.htm) deals more with the main processor/memory bus.

The system bus is the main lines of communication between the CPU, memory and all other components. PCI, ISA and VLB are local buses, transferring data from periferals to the system bus. Kind of like the feeder roads to the loop around a large city...

PCI is considered a better bus for several reasons, mainly that it is faster, and carries more data at once than ISA. ISA is still in use, and is often sufficient for some components, such as modems, and often sound cards. It is being phased out in favor of PCI by the manufacturers slowly, in most modern PC's you'll find only one ISA slot, and sometimes none.



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[xor_chad]

Hey
The links to PCGuide say it all about buses.

However the 'how does the cpu run faster than the bus' question is not covered...i dont think.

Its as simple as you deducted it. Lots of buffering and lots of wait states. If the CPU were to run at EXCATLY the same bus speed then there would be lots of wait states because of the number of cycles per instruction.

I personally think a double internal bus would be ideal.
Like memory bus at 200MHz and cpu internal bus at 400MHz.

Feel free to ask any questions the articl didnt clear up. Maybe we can help. LAters...

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Chad Wilson
C++/ASM Programmer
PC Support Technician