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FSB and multiplier. is my understanding correct?

post #1 of 4
Thread Starter 
Am I correct that the FSB speed is between 1mhz-650mhz or even more.
And the FSB speed of the motherboard is depended on the FSB speed of the CPU.
and the speed of memory ram is also depended on the FSB speed of the CPU, but it has its own independent multiplier
and the part of CPU which does the calculations has its own multiplier too

For example there is a motherboard with a CPU which has FSB of speed of 200mhz, but its multiplier is 4 so the actual speed of motherboard and CPU is 800 mhz.
the memory has multiplier of 2 so the speed is 400mhz
and the part of cpu which does calculations has multiplier of 24 so the actual speed is 4.8 ghz
post #2 of 4
You're close.

FSB (Front Side Buss) is the speed at which the various components on a motherboard communicate with other.

For a CPU: FSB x Multiplier = CPU speed
For Memory: FSB x Divider (kind of like a Multiplier for memory) = Memory speed.

So, if you change the FSB, you change the CPU speed and the Memory speed.
By changing the Multiplier and the Divider you can change the CPU and memory speeds independently of each other.

FSB is limited by the capability of the motherboard.
CPU speed is limited by the capability of the CPU.
Memory speed is limited by the capability of the Memory.

Modern motherboards allow the independent setting of the CPU and Memory speeds (unganged mode).

It's really a lot more complicated than the above, but that's basically how it works.
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post #3 of 4
Thread Starter 
But doesn't CPU have its own FSB which has to be the same as the motherboard's FSB???
post #4 of 4
Quote:
Originally Posted by mpw94 View Post

But doesn't CPU have its own FSB which has to be the same as the motherboard's FSB???
No. And yes.

CPUs have a buss speed (most AMDs use 200mhz.).
When a computer boots up, the BIOS reads that speed from the CPU along with how fast it's supposed to run, for example 3.0GHZ. The BIOS will then automatically pick a FSB that will make the CPU run at it's specified speed. (200Mhz buss speed X a 15 multiplier = 3Ghz, for a 3Ghz CPU)

Of course you can override the BIOS's choice (if you have an overlockable motherboard) and pick a FSB of, say, 201. Then the CPU will run at 3.015Ghz (201 x 15 = 3.015).

Note that changing the multiplier by one number, ie. from 15 to 16 (200 x 16 = 3.2GHz) makes much larger changes to CPU speed than does changing the FSB by one number (201 x 15 = 3.015Ghz)
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Overclock.net › Forums › General Hardware › General Processor Discussions › FSB and multiplier. is my understanding correct?