System Builder: Overclocking 101 – General – How To

We uncover the basic concepts behind modern overclocking.

If you’re a little short on change, but desperate for a little more grunt under the hood, overclocking your CPU has been a method commonly used by PC enthusiasts for well over a decade. The difference between overclocking ten years ago, and overclocking today, is the benefits are far more substantial, and the techniques involved are much easier to follow.

Unfortunately there is no universal guide that can be followed, so we’ll do our best to explain the fundamental principles of overclocking, in the hopes that you can explore your BIOS and identify the important settings and eventually understand their impact on both system performance and stability.

Front Side Bus
Not every system has a Front Side Bus. It was a technology originally used by Intel, though AMD and even newer platforms that no longer use the technology often still have FSB listed in their BIOS to make it easier for the customer to identify the primary bus connecting the CPU to mainboard critical components (such as RAM).

In newer Intel systems, the FSB is sometimes called Blck, and AMD systems may use FSB or HT. Essentially this is the speed at which your CPU can communicate with the motherboard chipset and all that it controls. In the case of many newer Intel motherboards, the link is now only between the CPU and RAM.

The higher the frequency (MHz), the larger the bandwidth between your CPU and motherboard chipset.  Think of this like a highway. Increasing the MHz is like adding more lanes to that highway, and will allow more traffic to pass through at once, thus increasing the potential for greater CPU and memory speeds.

Using the same analogy of cars on the highway, let’s say each signal sent from the CPU is a car. The faster these cars are going, the harder they are to track. For this reason, increasing the voltage enhances the signal strength of each car, making them easier to track, resulting in less accidents or “corruptions” in memory and CPU calculations. Higher voltage is necessary when increasing the frequency of any PC component.

It’s all well and good to have a more advanced road (wider bus) for your CPU traffic, but unless you’re processor can generate enough traffic for that road there isn’t a whole lot of point to overclocking the FSB/blck/HT of your system. This is where the CPU clock speed (MHz) comes in.

Every CPU has a process called a “clock cycle” and it is essentially a series of steps the CPU goes through in order to calculate and process data. The faster the CPU can carry out these steps, the faster the data is calculated. Simple, right?

The objective of overclocking a CPU is to raise the clock rate (work rate) to a level higher than the factory settings. This allows users to “unlock” free performance that only more expensive CPUs are normally capable of. This could be as little as 5% gains or as high as 50%, depending on how much time you’re willing to spend learning your individual CPU, and also how much money you’re willing to spend on cooling solutions.

When overclocking a modern day CPU, you will either be controlling the clock rate by a number called the “CPU multiplier”, or by the “Front Side Bus” (see above). The CPU multiplier is found by dividing the speed of your processor by the frequency of your Bus. For example, if your processor is a 2.4GHz (2400MHz) CPU, and your BIOS tells you the bus speed is 100MHz, your CPU multiplier would be x24 (24×100=2400). Similarly, if you’ve increased your bus speed by 5MHz, now reading 105MHz, your CPU will automatically increase in speed due to the multiplier. It should now be reading 2.52GHz (2520MHz) (24×105=2520).

Before you jump into your BIOS and have a look at how much faster your CPU can run, you need to identify your system. Unfortunately, not all systems have an adjustable CPU multiplier, and some can’t even adjust the FSB/Blck. The new 3rd Gen (Ivy Bridge) Intel chips can only be overclocked if you’re on a P67 or higher chipset, and also using a “K” series CPU. If you’re not running either of those, you won’t have complete control over your system.

For AMD users, you will often have a little more headroom when overclocking. Generally speaking, most motherboards and CPUs should allow limited control over the CPU multiplier and bus speed of the board. Black Edition CPUs will allow for greater control, and they have an unlocked CPU multiplier (just like “Extreme” and “K” series from Intel).

Most modern day overclocks on the CPU are done using the CPU multiplier, not just by increasing the FSB, as was quite common in the Core 2 Duo days (and earlier). If you don’t have a CPU with an unlocked multiplier, there is usually still a small amount of headroom and a few points you can raise the number by before becoming locked at a cap. This is due to Turbo Functions on many modern day CPUs. Unless you want to start overclocking almost exclusively with the CPU bus, you unfortunately won’t be able to take your “locked” CPU too far beyond the stock and turbo clocks of the CPU.

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