Using CPU Level Up carries some risks. For example, though we're using an unlocked CPU, the BIOS setup assumes that the multiplier is locked. So instead of increasing the clock multiplier, the CPU level up boosts BCLK to 160MHz at the 'Crazy-3.52G' setting--and that alters memory timings.
Though our particular CPU was stable at 3.52GHz under stress testing, we recommend sticking with the 3.2GHz setting. That's almost certain to yield a successful overclock with this CPU, and it pushes BCLK to a less aggressive 146MHz. The memory speed isn't much greater than the default 1066MHz, but it is a little faster, at 1170MHz.
Now let's look at manually overclocking an Intel Core i5-750. This quad-core CPU's default clock speed with all four cores running is 2.66GHz. We'll use the Gigabyte GA-P55-UD4 for our exercise. Once you understand how multipliers work, the manual process is pretty easy. Let's take a look at a typical BIOS setup screen.
The expandable screenshot at right shows the advanced frequency settings screen in the Gigabyte P55M-UD4 BIOS setup program. To access this program, press Delete during bootup. We're concerned with three settings: 'CPU clock ratio' (the CPU multiplier), 'BCLK frequency' and 'System Memory Multiplier'. The default values are 20X for the CPU multiplier, 133MHz for the base clock, and 8.0 for the system memory multiplier.
We were able to easily push the Core i5 750 to nearly 3.5GHz by setting BCLK to 166MHz. This also pushed up the memory frequency to 1328MHz. Our more extreme overclock proved successful, but this system had already been running well for months with the following settings:
· CPU clock ratio: 20X
· BCLK: 150MHz
· System memory multiplier: 8X (yielding a memory speed of 1200MHz)
This particular setup has been rock-solid for us at 3.0GHz, running the stock Intel retail cooler.
Now let's look at the AMD system.
The Phenom II X6 1090T processor already runs at 3.2GHz, so pushing it up a couple of speed grades means running the system at 3.6GHz. So we'll set a limit of 3.6GHz using a fairly high-end CPU cooler, the $50 Thermalright Ultra 120 rev C with a fairly stock 120mm fan.
First, let's look at how the BIOS screen appears before we tweak the settings. The expandable screenshot at left shows this screen.
Although the settings for this AMD-based motherboard are similar to those for Intel-based motherboards, they are just a little different. The key items to consider for purposes of overclocking are the CPU ratio and the DRAM frequency.
Our final setting screen is shown in the expandable screenshot at right.