I don?t understand Intels 6850?s 1333 MHz FSB

[Chamade]

The reason why I don?t understand it is because of this.

If you take a look here http://www.anandtech.com/cpuch...howdoc.aspx?i=3038&p=3 it seems that they have used Corsair XMS2 DDR2-800 4-4-4-12 (1GB x 2) memory while they?ve tested the Intel Core 2 Duo E6850 CPU and doesn?t you need a memory who can handle 1333 MHz for that CPU and not only 800 MHz?

The reason why I wonder is because I want to know if I can buy a 6850 DualCore CPU with the 1333 FSB MHz and run that CPU on an Abit IP35-Pro motherboard with some 8500 DDR2 memory and knowing that it?s gonna work okay and that it?s giving me the speed I want and that nothing ?crazy? are gonna happen.


?crazy? = Something that puts a break on something in my computer.

 

[nyker96]

I think if you run 1:1 FSB1333 = 333 base FSB or so you just need DDR2-667 for it to run 1:1 or 800 if you adjust divider.

 

[GuitarDaddy]

The 1333 FSB is "quad pumped" which means the base FSB frequency is 333mhz (1333/4)

Intel mother boards run the memory on a ratio to the base FSB frequency, with the lowest setting on most boards being 2.0 also called 1:1. Using the lowest ratio the stock 333mhz base frequency gives you DDR667 (333x2).

So with a FSB1333 chip and DDR2-800 memory you can overclock from 333 to 400(base frequency) and still run the memory at stock speed or less. And most DDR2-800 memory will overclock quite well, letting you take it upwards of 450mhz.

 

[myocardia]

Welcome to anandtech. The reason why it's hard to understand Intel's FSB's, is because they aren't actually true. The stock FSB on the E6850 is 333 Mhz. That means you only need 333 Mhz/667 DDR2 RAM for them, unless you're wanting to overclock the CPU. It also means you can run an E6850 @ 3.6 Ghz, without overclocking PC6400 (800 DDR) RAM. Now, Intel isn't actually lying, because the chipset transmits data 4 times per clock cycle, so it actually performs roughly as well as it would if it ran @ 1,333 Mhz, but only transmitted data once per clock cycle.

 

[Denithor]

Intel CPUs are "quad-pumped" so their chips run at 4 times the FSB. In the case of the e6850 this equates to 333x4=1333MHz. The processor speed is based on the FSB and the chip's multiplier, in the case of the e6850 the multiplier is 9 so at stock speed it runs 3.0GHz (333x9).

DDR/DDR2 memory runs at twice the FSB so DDR2-800 memory is rated to work at up to 400MHz FSB (400x2=800MHz).

Therefore the e6850 at 333MHz is actually a perfect 1:1 match for DDR2-667 memory. You really only need to buy DDR2-800 (or higher) rated memory if you plan to overclock the system by increasing the FSB. If you increase the FSB to 400 the e6850 will run at 3.6GHz (400x9) and your DDR2-800 will run at the stock speed.

However, you are probably better off buying the e6750 (4MB cache, 333x8=2.66GHz) for $100 less than the e6850 and overclocking to the same point (375x8=3GHz) or even faster (400x8=3.2GHz). Typically most DDR2-667 memory can handle up to 400MHz speed but to make sure you could get DDR2-800 rated memory. The stock Intel cooler will handle 3GHz, above that (regardless of the processor) you probably want to use improved cooling.

Overclocking is extremely easy and stable on Intel processors if done correctly. There are several great overclocking guides here on the forums if you need help.

 

[Chamade]

Thanks a lot friends.

Great answers and now I understand it.

*Happy Happy*