FSB and Multiplier

[speedy742j]

I have - what to some - might seem like a simple question; however, I can't seem to get a straight answer about it.

How do FSB and multiplier relate in overall speed? Let me explain...

When I run Flight Simulator (a CPU intensive game opposed to GPU) with my system clocked at 3.4ghz (9x378) the frame rate is slightly less than when I run it at 3.2ghz (8x400). Why is this? I would expect the first senario to be faster.

Hence, I am wonder if someone could explain why this is, and if this is to be expected.

Thanks.

 

[serpent1202]

Speedy. Are you making any changes to your memory divider or are you simply adjusting FSB & Multipier. You ram is probably set at 2:1. So when you set your FSB to 378, your RAM only runs at 756 MHZ. By setting your FSB at 400, your RAM runs at its rated speed of 800 MHZ creating a better cpu experience.

This is assuming you have 800 mhz ddr2 ram, which 95% of people have.

 

[MaDMagik]

Also with higher bus speed the data transfer to/from cpu is quicker, which might be the factor here. I guess the memory ratio is actually 1:1 since 400mhz fsb results in DDR2 800. With cpu speed differing only by 200mhz I would always go for the 400 mhz fsb.

 

[speedy742j]

I think I'm being a little lose (unintentional) with terms. Sorry about that...

My CPU clock ration is 8x and my CPU Host clock control is 400mhz. The system memory multiplier (SPD) is set to 2.00D (not sure what the D means?!).

Serpent - you are right - when I set it to 738 I do get 756mhz. yes, I am using G Skill DDR2 800mhz.

So, is the 8x400 a better combo than the 9*378? If I try to run 9*400 (3.6ghz), then the system restarts as soon as prime95 starts working.

Thank you guys.

 

[MaDMagik]

Yes, 8x400 is better. But if you can load windows at 9x400 than probably you will just need to increase cpu core voltage to make it stable. Read the overclocking guide in this section, its very useful. Or even better find some guide thats based on your motherboard.