Confused about FSB speeds and why my system won't boot...

[BigToque]

I've got:
Asus P5Q Pro
Intel E5200 - Totally stable at 3.2 GHz (12x266)
DDR2-1066


My problem is:
In order to run my RAM at a 1:1 ratio with the CPU, the FSB needs to be bumped to 533 MHz.

Right now my memory is running at 1:2.

If I bump the FSB to 533 and drop the multiplier to 6 (for a speed of 3.2 GHz that I know the CPU can handle), which would make my ram run at 1:1, the system simply will not boot. It just blank screens until I reset the bios.


My question is:
Why will the system not boot with a 533 FSB? I've got options from 200-800, so I assumed a setting of 533MHz didn't seem strange.

Is my memory destined to be running at 1/2 speed, or am I just not doing something correctly?

 

[Painman]

A raw 533 MHz FSB is WAY more than the P45 chip is designed to deal with; that's the beginning of your problems.

The math is a little "fuzzy".

Your CPU's FSB isn't really 533. Not as far as the P45 is concerned. It's 266.

There are multipliers you can choose for mem speed... you already know this... more on that later.

With a multi of 12 or less, choose your CPU OC. Let's suppose (but not assume) it'll do 4.0 GHz. So Set the FSB/Multi to 400/10.

At 1:1, that'll give you a RAM speed of DDR2-800. 400 * DDR2 = 800

At 5:6 (oftentimes it's listed backwards) you'll get (400 * (6/5)) = 480 = DDR2-960.

Try 3:4. (400 * (4/3)) = 533 = DDR2-1066.

Hope that helps.

 

[n7]

...or am I just not doing something correctly?

Your first mistake is thinking you need to be running 1:1.

That aside, your CPU is never going to hit anywhere close to 533 FSB.

You've got a 200 FSB CPU, & those tend to make to it around 300-400 before reaching their max.
266/333 FSB CPUs will get a lot higher than yours will.

On your board, i'd bet on somewhere around ~ 350 FSB being the highest it'll get. This is somewhat a CPU & somewhat a board limitation with such a CPU.

Anyway, stop worrying about 1:1.

1:2 gives you your rated RAM speed of 533 (DDR2-1066), which is where things should be.

Pro tip for P45 OCing:
You want your FSB as high as stably possible (in your case, this will be below 400 more than likely), your RAM as high as stably possible (not 1:1), with tRD (Performance Level) timing set manually as low as possible.

Here's what i run my E5300 at.

 

[zagood]

BigToque, good info from these guys. I'd also recommend reading the "How To" sticky for a more in-depth look at overclocking and how FSB/Memory interact: http://forums.anandtech.com/showthread.php?t=47089

One major point - just because your motherboard has a wide range of settings doesn't mean your hardware can handle it. For instance, your voltage options will go way higher than your chip can handle - I wouldn't recommend going above 1.4v for 24/7 operation on the e5200, and definitely stay away from 1.5v and above.