Please explain FSB vs. ram speed

cadder

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Nov 17, 2008
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I read lots of people that run their FSB at faster than 400MHz. It seems to me that most DDR2 is rated at 800MHz, so how does this work?

Do you overclock the ram at the same time?

Do you run a ram multiplier of less than 1:1?

I'm not an extreme overclocker so I just assumed that I would stop when my FSB reached 400 and leave it at that.
 

idisarmu

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ram runs at double your base fsb clock.

Most ram is PC5300 in cheap computers or non-oc'ed pcs from dell/hp/acer etc... or at least I hope... DDR2 533 is useless.

If you have pc6400 (800mhz ram) and you put your fsb to 333 with a 1:1 ram divider- the ram will run at 667 (pc5300 speeds)

If you put your fsb to 500 (highest fsb that some mobos support) the ram will automatically overclock itself to 1000mhz (PC8000 speeds... almost pc8500 ddr2 1066)

Some mobos will let you change the ram divider ratio so that for example: you can run a 450fsb on PC6400 without burning it up. (or vise versa... you could run a 333fsb with PC6400 and cahnge the memory divider so that the ram runs at ~full speed....

That's what I know at least from reading stuff on here and trying my own overclocking.
 

4745454b

Titan
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Sounds right. I didn't see anything that needs correcting, hopefully cadder understood it. To answer his question directly, you can do either one. You can overclock your ram as you bump it up, or your can change the ratio so that it stays in spec. Its up to you. If your not an extreme overclocker, then just leave the FSB at 400.
 

cadder

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The reason I ask is that it seems that most quadcores have lower multipliers than the dualcores. I have the FSB at 400 in my E8500 machine and feel like I'm not missing out on much, but some of the quadcores probably won't reach their limit until you take the FSB above 400.
 

4745454b

Titan
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Thats probably due to heat. As I mentioned in a different thread, most of Intels quads top out at less then 3GHz. 2.33-2.8 is where most of them operate at. The 8400 starts at 3.0GHz, you can get faster like your E8500 for example. All of these use the same 1333 bus (333 actual), but 4 cores running at 3.0GHz is a hard thing to cool. I'm not sure what you mean by "reach their limit", but a Quad even on 333 is good.
 

cadder

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I'm thinking about what you can get the processor to run at without the last few percent of pushing and really upping the vcore. For instance I set a goal of 3.8GHz for my E8500 even though I expect if I really work with it I could probably get to or exceed 4GHz. A lot of people seem to get their quadcores up to 3.6GHz territory if they work with them, and this requires FSB beyond 400 or multiplier beyond 8.