|Introduction to Overclocking Guide for Beginners|
|Articles - Featured Guides|
|Written by Vito Cassisi|
|Thursday, 13 March 2008|
Page 6 of 13
DDR RAM Overclock Details
To help explain how these ratios/dividers work, here is an example of a 1:2 ratio:
Firstly, imagine 1:2 as ½, so:
RAM (with 1:2 divider): 400MHz (Bus Speed) x ½ (divider) x 2 (DDR) = 400MHz
NOTE: Remember that the HT Bus (AMD systems only) is equivalent to the Bus Speed in Intel systems. Substitute the terms if using an AMD setup.
As you can see, when the 1:2 divider is on, the RAM speed is halved while the CPU speed stays the same. The divider does not affect the CPU, only the RAM. That particular divider isn't too much use for this example because the RAM becomes severely underclocked.
Let's assume that we know that the CPU can perform 3.6GHz safely (with a multiplier of 9) and the limit for the RAM is 800MHz (RAM stock speed is 667MHz and CPU stock is 2.6GHz). How can we achieve this optimally while allowing for further overclocking? Well using basic maths, 9 x what gives us roughly 3.6GHz? A 400MHz FSB does, so:
RAM: 400 x 2 = 800MHz
To fix the problem with the limited RAM we can use a 5:6 (ÃƒÆ’Ã‚Â¢ÃƒÂ¢Ã¢â€šÂ¬Ã‚Â¦Ãƒâ€¦Ã‚Â¡) divider:
RAM: 400 x ÃƒÆ’Ã‚Â¢ÃƒÂ¢Ã¢â€šÂ¬Ã‚Â¦Ãƒâ€¦Ã‚Â¡ x 2 = 667MHz
Now the RAM is at stock but the CPU is overclocked to 3.6GHz. Because we don't know the limit of the CPU, we can keep going until it is unstable (reaches its limit). Now the RAM still has quite a bit of headroom to allow the CPU to be pushed further without reaching its limit.
Let's say that after vigorous testing we get the CPU to 4GHz:
RAM: 444MHz x ÃƒÆ’Ã‚Â¢ÃƒÂ¢Ã¢â€šÂ¬Ã‚Â¦Ãƒâ€¦Ã‚Â¡ x 2 = 740MHz
This is where tweaking comes in. If the multiplier of this CPU is unlocked, we can do the following instead:
RAM: 400MHz x 2 = 800MHz
Now both the RAM and CPU are performing at their optimum speed. Now you're probably thinking "Why didn't I just increase the multiplier in the first place?!" That's because you didn't know that CPU could handle 4GHz (see the multiplier section above which uses the same example). With the RAM dividers you were able to slowly see what the CPU limit was without jumping from 3.6GHz straight to 4GHz. The CPU could have reached its limit at 3.8GHz, so the multiplier alteration would not help find a stable clock.
Determining the Limit of the CPU & RAM - Stability
With all this talk about device limits and instability, you should be wondering "How the heck did you figure out the ‘limits'?" or "How do I know the PC is unstable? And how do I test if it is?"
The limit of a CPU is determined when you overclock it and it gets to a point where it becomes unstable. Voltage increases will to an extent allow further overclocking, but when this does not help anymore the true limit is reached.
To determine system stability, programs like Orthos Prime & OCCT are used. Orthos Prime stresses both CPU and RAM to see if they are stable. If Orthos Prime can run a couple of hours without the PC freezing, rebooting, or Orthos complaining, then the PC is considered stable. While the stress test is running, it is good to keep track of the temperature. Running software such as Core Temp in the taskbar allows you to monitor CPU temperatures. Remember, anything over 60oC for a CPU is not recommended, and 70oC+ is getting a little dangerous. OCCT works the same way as Orthos, but it is generally more up-to-date. OCCT can be downloaded here, while Orthos Prime can be obtained here.