cpu-z says memory frequency is 266 MHz, BUS speed is 266 MHz, while FSB is 1066 MHz...what’s the difference between BUS and FSB (beside the obvious speed discrepancy)?
It sure is hard to tell sometimes, I'll give you that. Whoever came up with the current naming scheme used to describe the parts connected to the processor bus seems to have wanted to maximize total confusion. (Ah, marketing!)
The one important speed to keep in mind, the one which determines what all the other clock speeds turn out to be, is what I'll refer to as the system clock speed. In the case of a Core 2 CPU running at stock, this is 266MHz. This is the speed that is multiplied by the "multiplier" of the processor to get the actual speed the processor runs at. In the case of an E6300, the multiplier is 7 so the CPU runs at 7*266 = 1,862 MHz or 1.86GHz.
Now I frequently also refer to this "system clock speed" as the "FSB". I probably shouldn't but I do simply because the two are so tightly coupled. The actual or effective speed of the FSB is simply 4 times the "system clock". In this example that is 4*266 or 1,366MHz effective speed. Why four times the system clock? The FSB is "quad-pumped" which appears to mean that 4 units of data are actually transfered on the FSB for each tick of the system clock.
How is this "quad-pumping" done? I have no idea. Is it related/coupled to dual channel memory? Seems likely, but again I really do not know how it works. All I know is that the effective FSB speed is 4 times the system clock speed. However this
does seem to dove-tail really nicely with both dual channel memory and DDR DRAM supplying 2 units of data per clock tick. 2 (DDR) * 2 (dual channel) = 4 (quad-pumped).
And then there is your DRAM. The timings there work out as you outlined them. CPU-Z shows the base clock speed, not the effective speed for your DDR memory. You have to multiply this value by 2 to get the DDR2 rating. For example, 2*266 implies DDR2-533.
Depending on the motherboard and BIOS, it is possible to run your memory at a different clock speed than the FSB/system clock is run at. Usually you'll be advised to not do this because running the FSB and DRAM at the same speed (a FSB
😀RAM ratio of 1:1) usually gives you the best throughput.
But as an example, in your case your RAM is DDR2-667 so it can run at a base clock speed of 333MHz. If your BIOS allows it, you could leave the system clock at 266 but run the memory at 333. If you did this the FSB
😀RAM ratio would be 4:5 (I think ... :? Understanding the concept and getting the arithmetic right are two separate issues for me).
Now why not run your RAM at it's fastest speed? Because this will only increase the performance of your system if the RAM speed is your only bottleneck. Usually it isn't, the FSB is. So often instead of running their system clock at "stock" and running their RAM at a higher speed people will instead overclock. If you up your system clock to 333 and maintain a FSB to DRAM ratio of 1:1 your memory will run at it's full rated speed. But you will also get a much larger performance increase from running your CPU at 7*333 = 2,331MHz or 2.3 GHz.
I seem to have run off at the mouth on this reply. Hope what I've said helps some. If it doesn't, just ignore it.
Someone else will probably explain it better. This stuff is constantly being rehashed on these boards. Like I said, it is almost as though it was designed to confuse people.
-john
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