Question on Frontside Bus

[bradacus]

I need a hardware mentor! I swear I overthink simple things.

When I read a CPU specs and it talks about FSB speeds. Does that mean that it supports those speeds (from mobo manufacturers)? Or does it mean those speeds are internal within its own line (L1/L2) cache?
I ask because if it is talking about its own cache then doesn't that mean BSB speeds (backside bus).
I was under the assumption that FSB was the speed of the address bus to the memory controller chip accross the RAM interface to the RAM. Which would make those speeds motherboard specific right?
Or does the CPU control the speed of the bus on the motherboard? Kind of like the CPU provides the car and the motherboards address bus provides the street?

I think I am a bit confused. Can anyone sort me straight on this?

 

[dragonsprayer]

no

fsb is a wide range - you want a 2:1 ratio

so if your cpu is 1600 your memory is 800 at 4-4-4-12 or less

fsb is the conection between the nb and cpu and memory - does not matter what specs are posted as long as you set your system to the optimal settings

cd2 mutliper of 9-10 (10 for extrme cpu's)
memory at 2:1

fsb1600 and memory at 800 for ddr2

ddr3 1600 plus or minus 100

 

[bradacus]

Does the CPU control the FSB speed? Or is it all dependant on the motherboard?

 

[dragonsprayer]

no

 

[dragonsprayer]

The fsb speed overrides both the cpu and memory

so if your cpu is 3ghz and your memory is 800 ghz and you raise the fsb by 10% then the memory and cpu go up by 10%

fsb 1066 cpu = 3ghz mem = 800mhz

10% boosit ==
fsb 1172 cpu 3.3ghz mem = 880mhz

choose a q6600 (or e6600) at 2.4ghz at ddr 1066 and boost it 1600 with ddr 800 memory =

fsb 1600
cpu = 3.6ghz
memory=800mhz at 2:1 ratio

you want even numbers not fractions for memory

at 1500 fsb

you have
3.4ghz
memoy = 750

memory at 700-900 ddr2 is ok with low latencies

-----------------------------

ddr400 2-2-2-8= optima = 2-2-2-5
ddr2800 4-4-4-15 = 4-4-3-10
ddr31600 8-8-8-24 optinal = 7-7-7-20


ddr3 = ddr2=ddr when the latecies are factored in - -this is really bad but research it

 

[cjl]

The FSB speed is set by the CPU specifications. By default, the motherboard will run at whatever FSB the CPU is specified at. Dragonsprayer is talking about overclocking.

Oh, and dragonsprayer: DDR3 does not equal DDR2 does not equal DDR when latencies are factored in. They do have roughly the same latencies, time wise (the latencies are rated in clocks, so DDR2-800 with a 4 cycle latency and DDR3-1600 with an 8 cycle latency will both have exactly the same true latency), but the newer ones have much higher bandwidth. Latency is not the only important factor.

 

[Mondoman]

To clarify, Intel CPUs (except for the new i7) have their memory controller on a separate chip, the "northbridge" part of the chipset. The FSB is the bus that connects the CPU with the northbridge. The memory bus is completely separate, and connects the northbridge's memory controller with the RAM DIMMs. Thus, all data transfers between the CPU and RAM go through the FSB, the northbridge, and the memory bus. Whichever of those has the lowest max throughput is the bottleneck. Normally, that's the FSB.

The CPU core and FSB speeds are set based on a base frequency provided by the motherboard. The CPU's core speed is a multiple of the FSB base freq. Thus, to adjust the CPU core speed, you can change the FSB base freq, and/or change the multiplier. Intel normally locks the mutiplier in its CPUs to a maximum value specific to each model. "Extreme" models normally have unlocked multipliers.

Premium motherboards designed for overclocking have options in the BIOS to manually change the FSB base freq and often the CPU multiplier. Standard MBs just identify the CPU chip and set standard freqs based on that ID.

 

[Mondoman]

To further clarify, the memory bus and FSB are completely independent of each other and can each be adjusted separately. If you like, you can have the memory bus speed vary proportionally with the FSB via a BIOS option (this may be the default option on some boards).