Section 2: Explanation of the Basic Settings
The first thing you want to do is explore the menus and settings in your BIOS. There are several very important settings that you want to find and familiarize yourself with, and many other settings that you won't change or need to know much (if anything) about. Let's go over the settings that you'll likely have to manipulate while overclocking.
Reference Clock
This is the setting that starts at 200 and is increased to overclock your computer. This is the single most important setting, as the CPU, HT Link and memory all reference this number when calculating their speed. The reference clock is often incorrectly referred to as the FSB, which is an Intel term that has no bearing on AMD 64 X2 systems. The reference clock is also referred to as the HT, HTT, CPU speed, and many other terms that aren't really correct, however many people and motherboards use them. It is important to note that unlike Intel's FSB, no data is actually transferred on the reference clock. It is merely a number created by the clock generator that other devices reference to calculate their speed. Your motherboard should give you the option to increase the reference clock by any whole number, up to a certain max value such as 400 (i.e. Auto, 200, 201, 202, 203, …, 398, 399, 400). It is usually a bad idea to increase the reference clock by any more than 10MHz at a time, as large changes can cause your system to fail to post.
CPU Multiplier
This setting decides what number will be multiplied with the reference clock to determine the total speed of the CPU. The setting usually starts at 5x, and can go as high as 16x (some even higher). Some motherboards will only allow whole number multipliers (i.e. Auto, 5x, 6x, 7x, …, 14x, 15x, 16x) whereas others allow half multipliers as well (i.e. 5x, 5.5x, 6x, …, 15x, 15.5x, 16x). As an example, say the CPU multiplier is set to 10x, and the reference clock is overclocked to 215. Your computer will determine the CPU speed as 215 x 10 = 2150MHz. If you increased the CPU multiplier to 11x, the CPU speed would be 215 x 11 = 2365MHz.
HT Multiplier
This setting helps determine the speed of the HT Link, which controls the speed of input/output devices on the motherboard. Most motherboards have a whole number multiplier ranging from 1 to 5 (i.e. Auto, 1x, 2x, 3x, 4x, 5x). The HT Link is determined by multiplying the reference clock with the HT multiplier. Most AM2 motherboards run at 1000MHz by default, meaning that a system that has not been overclocked yet has a reference clock of 200 and an HT Multiplier of Auto (which automatically sets it to 5x), giving 200 x 5 = 1000MHz. As you increase the reference clock to overclock your system, the HT Link will rise to values exceeding 1000MHz. At some point, the HT Link will reach a value that is so high that your system will either become unstable, fail to load Windows, or fail to post. You can bring it back down to a reasonable value by lowering the HT multiplier to 4x or lower. Many AM2 motherboards can run at very high HT Link speeds, such as 1200-1400MHz. However, there is no advantage to running the HT Link at anything above 800MHz, so don't be afraid to lower the HT Multiplier to regain stability. Overclocking the HT Link past 1000MHz won't improve system performance. Some motherboards will list this setting as (Auto, 200, 400, 600, 800, 1000). Note that these correspond to the 1x, 2x, 3x, 4x, and 5x multipliers respectively.
CPU Voltage
Also called vCore among other names. This setting controls the voltage given to your CPU. Depending on the motherboard, this setting can have a wide range of values. Most AM2 CPU's have a stock CPU voltage of 1.30v, and can be safely increased to 1.45-1.50v assuming that you have an aftermarket CPU cooler keeping your temperatures low. When testing for the maximum CPU Speed (this process is described later) you can add stability to the system by increasing the CPU voltage by 0.0125v or 0.0250v increments. Just remember that more CPU voltage causes more heat, so keep an eye on temperatures and invest in an aftermarket CPU cooler for $20-45.
Motherboard Voltage
Also called vChip among other names. This controls the voltage provided to the motherboard's chipset. Increasing the motherboard voltage can add stability at very high reference clock and HT Link settings. Higher end motherboards might break this down into northbridge and southbridge voltages.
Memory Setting
This setting is one of the two major factors in determining the CPU --> Memory divider, and therefore a major factor in determining the speed of your memory. It will have options that look something like this (Auto, DDR2 400, DDR2 533, DDR2 667, DDR2 800). Some newer motherboards might also allow DDR2 1066. The other factor that determines the CPU --> Memory divider is the CPU multiplier. Calculating the divider and DDR2 memory speeds can be a little complex for socket AM2, so a few months ago I wrote up an explanation that you can read about here:
DDR2 Memory Speeds Explained.
Memory Voltage
Also called vDIMM among other names. This setting controls the voltage given to your memory. Every brand of memory has an internal circuit (or IC for short). Some popular memory IC's are Micron D9's and Promos. It is the memory's IC, not the brand of memory, that determines how much voltage the memory can take. Read more about memory IC's on
Enterprise's well written thread. Some IC's like 1.8-2.0 volts. Others, such as Micron D9's, like 2.1-2.3 volts. The same brand of memory might have used one IC in early versions, and a different IC in later versions. So make sure you know what IC your memory has and what voltage it can handle. Google search, check the Specifications on the web site you bought them from (if you just bought them recently), or ask someone here on OCN. Increasing the voltage to your memory can provide stability, but it's usually not a good idea to give them more than 0.1 volts beyond what they're rated for, and definitely no more than 0.2 volts. And as always, more voltage, more heat.
Memory Timings
These are often located in the same menu as the memory setting. There are many memory timings, but some motherboards only allow access to the most important memory timings, which is usually not a big deal. Unless you really know what you're doing, there's only a few memory timings you'll need to adjust, the rest you'll leave on Auto. Let's take a look at how memory timings are traditionally reported:
4-4-4-12which corresponds to:
CAS Latency - tRCD - tRP - tRAS
You'll definitely have to manipulate these timings, so make sure you find them in your motherboard. CAS Latency is often called other names, such as tCL. Another important timing that you should find is tRFC (there should be a tRFC for each memory slot, and are usually labeled tRFC0, tRFC1, tRFC2, tRFC3). You want to make sure that all tRFC values are set to the same number, such as 105ns. You'll also need to change the tRC so locate that setting as well. Finally, you'll need to find the command rate and make sure it is set to 2T.
Because the tRC and command rate are important settings, you'll often see me write my timings like this:
4-4-4-12-23-2T which corresponds to:
CAS Latency - tRCD - tRP - tRAS - tRC - command rate
Cool'n'Quiet
This feature is an overclocker's enemy. If enabled, it will underclock your CPU when your computer is idle. Make sure you find this setting and set it to disabled.
PCIe Clock
This feature controls the frequency of the PCI express slots. Lock it at 100MHz to make sure it doesn't interfere with your overclock stability. Some motherboards might not even offer this feature, so don't worry if you can't find it.
