Front Side Bus speeds

[jny4916]

Hey all,

I posted this on the computer help forum, but no one there responded.

I come from the old P4 days. Have not upgraded MB or CPU in 4 years. In those days my P4 2.8 ran at an 800 FSB. Which was really 200x4 since Intel calls their chipset quad-bumped. And the DDR ram ran at 200x2 for DDR400 which is PC 3200.

OK. So can someone explain the new FSB speeds for me? Are they running at x8? Which would be 2 cores x4? And if I dont buy the DDR3 1333 memory for my 6750 processor, do I have to change any of the clock speeds? Like if I buy DDR2 1066 it wont synchronize perfectly with the 1333 bus speed of the 6750 so the clock speed of the memory will run slower?

Anyway I think i have a pretty good handle on it, but if someone could shed a little more light on how Intel is clocking their processors I would greatly appreciate it.

Thanks in advance,

--Chris

 

[Shimmishim]

it's still the same

4X00 = mult x 200 (800 quad)
6X00 / 6X20 = mult x 266 (1066 quad)
6X50 = mult x 333 (1333 quad)

ram is same 2 x FSB so for the 6X50 it's 333 x 2 or 667 or pc2-5300

each core runs at the rated speed so a 6600 which runs 9 x 266 has 2 cores running 9x266.

 

[JustaGeek]

In addition to the above, the memory dividers can increase the speed of the Memory Bus, that is only then multiplied by 2, for DDR.

Example in my case:

325MHz FSB x 16/13 divider = 400MHz Memory Bus

400MHz x 2 (DDR) = 800MHz Memory speed.

 

[Shimmishim]

and to add to that.. 🙂

the available dividers depends on the chipset and board but the most common you will find are:

1:1 fsb/mem
4:5 fsb/mem
2:3 fsb/mem
1:2 fsb/mem

meaning fsb 266 mem 533 (266x2) for 1:1
meaning fsb 266 mem 667 (333x2) for 4:5
meaning fsb 266 mem 800 (400x2) for 2:3
meaning fsb 266 mem 1066 (533x2) for 1:2

these are the ones you will find on 975/965/P35/G33 (and X38)... plus the newer ones have 5:6 for 1333 FSB chips.

with the 680/650i chipset boards, you have unlinked dividers which means you aren't forced to these 4 or 5 divider options but can run fsb and mem at different speeds. i say unlinked dividers because it's not a true unlinked but forced ratios such as 15:16, 12:13, 11:12, 7:8, 9:10, etc... but a lot more than the 4 to 5 you are limited to with the previous mentioned chipsets

 

[jny4916]

OK that all makes sense.

If I choose a P35 MB with a linked divider, will I be forced into a memory overclock situation?

I think want to run a 1333 FSB on a 6X50 processor with DDR2 1066 memory.

Thanks again for the replies.

--Chris

 

[Shimmishim]

yes, that's perfectly fine since the stock speed of the memory is 533.

 

[jny4916]

OK... stock FSB speed is 333. Memory is tested up to 533. So there is tons of room for overclocking without stressing the memory.

 

[Shimmishim]

exactly! just leave it at 1:1. fine the sweet spot of the chip, then use a divider to increase you mem bandwidth! tada!

 

[jny4916]

yeah i dunno why i was getting confused. its still the same as it was before. I guess since they kept releasing memory speed numbers that matched the chip fsb speeds I started wondering if those had to match up. I completely forgot that the memory ones are multiplied by 2 and the chip speeds are multiplied by 4. So 1333 memory speeds are way unnecessary. And for most people DDR2 800 would be more than enough for a lightly overclocked rig.