How FSB's work

[Bojangles139]

k, so how do ram's speed, processor's FSB and the mobo's bus work together (does the processor speed affect the ram speed)? does the fact a board is dual ddr have any effect on ram's speed? does the ram and cpu have to have the same speed? also, why are P4's FSB's so much faster then AMD's?

brandon

P.S. i know the mobo will take any FSB in it's intended range, so the mobo's fsb is passive (meaning it becomes whatever the cpu's FSB is, correct)?

 

[paralazarguer]

I suggest that you read the FAQ before posting a thread next time.

Anyway, the Front Side Bus is the path that the processor uses to get information from the RAM.

A processor operates at a multiple of the front side bus. For example, a P3 1ghz might have a 100mhz FSB and a multiplier of 10. That makes it 100x10 or 1000mhz.

The EV6 bus of the athlon is double pumped. This means that it transmits data on both the rising and falling edge of the clock cycle so an athlon with a 133mhz FSB is eqivelent to a 266mhz FSB.

The pentium 4 is quad pumped so it transmits data 4 times per clock cycle so a 133mhz bus is equivelent to a 533mhz FSB. However, for multiplier purposes, it's a multiple of a true FSB speed (133mhz)

RAM is able to run asynchronously. For example, you can run DDR333 (which is a really 166mhz double pumped) with a 400mhz P4 system bus which is really 100mhz quad pumped.

Get it?

 

[paralazarguer]

(meaning it becomes whatever the cpu's FSB is, correct)?

No. The CPU doesn't have a locked FSB. for example, you can put an athlon XP1700+ which operates at 1.47Ghz and tell the motherboard to run at a 100mhz FSB. It will do this and the athlon will operate away at 1.1ghz. If you run the FSB at 133mhz, then it will run the processor will run at 1466mhz. If you run the FSB at 166Mhz, you will have a processor speed of 1826Mhz if the chip can handle that speed.
The processor is nothing more than a multiple of the front side bus speed. The frontside bus will not automatically set itself based on what processor is in the socket.

 

[tbates757]

System Buses Explained - Deviant PC

Enjoy.

 

[PCMarine]

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