Confused about FSB and RAM... 1066Mhz

[programmer]

I just picked up 2x1Gb of Crucial's PC2-8500 -- too cheap to pass it up. So now I am wondering how I can use it at its stock speed of 1066?

I need a motherboard and CPU and assuming I am not going to overclock, which combo is best to run this RAM at 1066? Is the RAM divider and FSB separate or tied in the BIOS, or is that different based on the manufacturer and model of motherboard?

From what I've read, I want a FSB of 266, but run the RAM at a 1:1 divider with the CPU (so CPU and RAM run at 1066, FSB is 1/4 that speed). Does that make sense??? And what is the impact of the upcoming 1333 bus CPUs? Should I consider the Quad core instead?

Many thanks for helping me decipher this stuff!

 

[n7]

Truth is, the RAM you bought is designed for use in overclocked systems.

Not that it can't be used w/ stock speed systems, but when you buy high end RAM like that, it's usually assumed you know how to set dividers/ratios.

Basically, w/ the current 1066 MHz FSB C2D CPUs, we have a quad pumped bus.
Simply put, it means the FSB speed is actually 266 MHz. (266 x 4 = 1066 MHz)
The "default" speed for matching RAM would be DDR2-533, or 266 MHz (1:1).

You bought RAM that's actually twice as fast as necessary, so if you were to run it with a stock CPU, you have to use one of the dividers, in this case, 1:2.

Therefore, your FSB runs at 266 MHz; your RAM @ 533 MHz (aka DDR2-1066).


Now to make things more confusing, nVidia's chipsets word things what i consider to be basically backwards, & they call running 1:2 1:1 instead...basing their ratios around the quad pumped FSB speed instead of the actual FSB. With many nForce chipsets you'll also have the ability to run RAM speeds indepenendent of the FSB, as in basically setting the speed to whatever you want.

 

[Heidfirst]

i believe that P35 mobos have the dividers necessary to run RAM @1066 with stock CPU fsb.

 

[programmer]

Ok, truth is I will probably overclock but was wondering if I could run the RAM at stock speeds. From what I've read, the P35 may allow 1066 DDR2 with a 1:1 divider, leaving the FSB at 266 (all stock), but I'm just not sure, and not sure which particular motherboards can offer this (apparently some don't offer the 1:1 divider option).

The GIGABYTE GA-P35-DQ6 looks like a very nice board, but more $$$ than I had planned on. The GA-P35-DS3R may be more the thing -- why does Gigabyte have so many P35 boards?!?! hehe

 

[programmer]

Note to self -- good options from Gigabyte are GA-P35-S3 (low end), GA-P35-DS3 (higher quality components), and GA-P35-DS3R (includes extended RAID modes). These are all DDR2 only, 1x PCI Express slot, and reasonably priced.

 

[renethx]

Originally posted by: programmerFrom what I've read, the P35 may allow 1066 DDR2 with a 1:1 divider, leaving the FSB at 266 (all stock), but I'm just not sure, and not sure which particular motherboards can offer this (apparently some don't offer the 1:1 divider option).

The GIGABYTE GA-P35-DQ6 looks like a very nice board, but more $$$ than I had planned on. The GA-P35-DS3R may be more the thing -- why does Gigabyte have so many P35 boards?!?! hehe

The 1:1 divider means FSBRAM Frequency = 1:1, so that if FSB = 266MHz, DRAM frequency = 266MHz, or DDR2-533. To run your memory at the DDR2-1066 speed (the I/O bus speed 533 MHz), you need to select the 1:2 divider.

• In the GIGABYTE P35 motherboards, the 1:2 divider = System Memory Multiplier 4.0+.
  
• In ASUS P5K Deluxe, the selectable DRAM frequencies are DDR2-667/800/889/1067MHz. Just choose DDR2-1066MHz. The corresponding FSB: DRAM ratio are
  
  • If FSB < 293 MHz, 4:5, 2:3, 3:5, 1:2
  • If FSB > 293 MHz, 1:1, 5:6, 3:4, 5:8
  That is, the strap change occurs at FSB 293 MHz.

 

[programmer]

Thanks, renethx (and n7 too, tho I didn't know what you meant by the 1:2 divider at the time)! That is just the information I was looking for.

 

[programmer]

Just to follow up, I picked up a Gigabyte GA-P35-DS3R and C2D 6420. Was delivered this afternoon (or yesterday afternoon at this point 12:15AM EST). Got it all put together and fired it up. Nice! The motherboard BIOS recognized the Crucial Ballistix RAM and set the memory speed to 1066 automatically, leaving the FSB at the stock 266. I'll get an OS installed and play with it a bit more tomorrow evening.