Overclocking CPUs

Performance tweaking to the extreme!

Overclocking CPUs was once seen as a black art deemed only of interest to the elite few in the gaming fraternity but is now a technique that anyone can employ with today’s latest overclock friendly motherboards that are on offer.

Processor overclocking was originally thought of as a very dangerous practice to the novice or intermediate user and only to be attempted by the advanced user to obtain the ultimate in gaming performance.

True, if you are not careful you could run the risk of frying your CPU and maybe your motherboard but with today’s components and the proper knowledge and a step by step process you can obtain vast increases in performance pretty much for free.

A 50% increase in CPU clock speed is easily obtainable and with careful tweaking and the right processor even more may be possible!

It’s not just for the gamers amongst us either, you can use the technique of overclocking CPUs to speed all of your processes, multitasking, encoding, virus scans, video editing etc.

We are now going to explain how to go about overclocking CPUs.

So, Just What Is Involved in Overclocking CPUs?

It’s all very simple really, processor overclocking is simply the term used to describe the process of increasing the clock speed of your motherboard and CPU and possibly your memory.

Your CPU operates at a stock frequency (default factory setting) in a multiple of cycles per second (Hz).

An Intel E8400 for instance runs at 3GHz stock speed (3,000,000,000Hz).

This is operating frequency is determined by an internal CPU multiplier of times 9 the motherboard FSB (Front Side Bus) clock of 333MHz, giving 3GHz.

How to overclock CPU?

Overclocking CPUs involves increasing the FSB speed by adjustment of the FSB setting from within the motherboard bios settings.

A good motherboard will allow you to increment the motherboard clock by maybe as little as 1MHz at a time.

Some older processors allowed you to adjust the CPU multiplier setting as well to obtain increases in performance but most modern processors are multiplier locked and the FSB adjustment is the only way to increase the operating frequency.

Intel for instance locks the multiplier for all but its Extreme Edition CPUs.

Now, increasing the FSB will eventually result in your PC becoming unstable if it is pushed too far and you will need to have some patience here in determining how far you can go.

Small steps are required one at a time and then you need to run a program which will exercise your PC to determine whether or not it is stable at this new increased clock frequency.

Increasing Voltage Settings for Stability

When you increase the processor frequency you may also need to increase the Core, Memory and Chipset voltages in small increasing steps of say 0.05V to ensure that your system will run stably.

This increase in voltage does not increase the operating frequency and hence speed of your CPU and system; it just helps to improve your system stability.

Beware though – this increase in voltage, if taken too far, can easily damage your components and will certainly raise component temperatures.

Never increase the operating voltages by more than 10% for your CPU and for your memory always check the manufacturer’s website to determine maximum allowable operating voltages.

This brings us to the next important point – heat!

All This Overclocking Is Getting Me Hot and Bothered!

This extra performance doesn’t come for nothing you know.

In order to increase the clock frequency we need to provide more power to the processor and with more power comes, yes you guessed it, more heat!

If you increase the operating frequency significantly you will almost certainly need to replace that stock cooler of yours with something a little more substantial!

A stock cooler will be designed to dissipate the heat of your CPU at its stock running frequency and they generally do so very well, especially the Intel Core 2 types.

Overclocking CPUs though will require the use of an aftermarket custom heatsink / cooler solution such as those available from Thermaltake, Arctic Cooling, Zalmon etc.

Modern processors do incorporate thermal protection and will slow themselves down if they detect that they are becoming too hot to prevent thermal runaway and eventual burning out.

Your processor should typically be operating around the 45ºC mark and certainly you shouldn’t be running higher than say 65ºC. If you are, you need to investigate a better heat sink option and also increased case ventilation.

Consider adding some case fans and ensure that your fans do not become clogged with dust and become inefficient.

Remember – there is no point in spending a lot of money on a fancy cooler when for the same outlay you could have traded up your current processor for the next model up!

Don’t Forget the Memory

Now let’s go back to the FSB (Front Side Bus) again.

Remember we talked about adjusting the FSB to increase the CPU operating frequency? Well, the motherboard FSB also determines the operating frequency of the memory.

With a decent motherboard your memory and CPU can be operated at the same frequency or can be adjusted to be asynchronous using a memory divider ratio.

For overclocking, the ratio should generally be kept at 1:1 operating frequency ratio although changing the divider setting can help keep cheaper memory in spec at higher CPU clock speeds.

If you are serious cheap memory isn’t really where it’s at and you should choose a high spec type from GSkill, Kingston, OCZ etc that will handle the increased frequency in its stride.

PC2-6400 memory for instance runs at 400MHz (800MHz DDR- Double Data Rate). With a standard un-clocked FSB of say 333MHz then a 6:5 frequency ratio will be required to operate the memory at 400MHz.

If the CPU is overclocked up to say 366MHz motherboard FSB frequency, keeping the 6:5 ratio will increase the memory operating frequency to 878MHz.

If you have high quality memory you may well be okay but if not you will need to adjust the divider ratio to say 1:1.

Changing to the 1:1 ratio will give you the option to increase your FSB even further if your processor will allow.

It’s All In The Timing

Memory isn’t just affected by the operating frequency you set for it but also your memory timings.

Your memory timings are dictated by the speed at which support circuitry operates at.

Memory latency settings determine how long the memory waits for operating states to settle before reading or writing at the next cycle of operation.

The lower the latency figure the faster your memory can operate at but faster operation increases the risk of error.

With cheaper memory the bios latency settings may need to be increased to achieve that higher overclock figure, albeit at the slight loss of performance.

Adjustment of the memory latency settings can be found in the advanced section of the bios.

CAS 5 is a standard latency figure quoted for DDR2 memory with a CAS 4 latency figure being quoted for high end memory.

Intel FSB

You will note that we have mentioned a FSB of 333MHz in our example above.

You may also have noticed that Intel quote an FSB of 1333MHz for the CPU.

All very confusing!

Well, this is all to do with Intel’s marketing of their Quad Pumping or quad data rate of operation.

Intel processors can complete four data transfers per motherboard FSB clock cycle so they class the processor FSB at four times the actual motherboard FSB figure. Really this should be stated as 1333MT/s (1333 mega transfers per second)

Therefore, for a motherboard FSB 200MHz, 266MHz, 333MHz or 400MHz Intel will quote an FSB of 800MHz, 1066MHz, 1333MHz and 1600MHz.


This is another bus used by your graphics card that is linked to your FSB directly.

Most processor overclocking friendly motherboards will allow you to set the PCI- Express bus manually to 100MHz and separate from the FSB.

AMD Athlon CPUs

AMD Athlon 64 CPUs do not use the FSB in quite the same way as Intel CPUs do.

The AMD processor has a memory controller built into it instead of in the form of a motherboard based chipset as the Intel CPUs do.

AMD motherboards still have a clock which determines the speed of data transfer between the CPU and the motherboard memory but the controller resides with the AMD CPU chip.

AMD uses HyperTransport as the Front Side Bus for their Athlon 64 and Phenom series of processors.

Confirming Performance Increase

How do you know how well your overclocked PC is performing against previous operation in its un-clocked guise?

Well, you need to establish a baseline by which you can compare results against.

To do this you can download and install various benchmarking programs such as:

3D mark 2001 SEPC mark 04Sandra 2005

Run the tests and record the results. This is your unmodified baseline. Now overclock your PC and when you are happy with it you can run the same tests again and compare your results.

Hopefully you have discovered enough about overclocking CPUs to give it a try yourself.

I'm sure if you do you will be extremely happy with your newfound increase in performance.

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