CPU Overclocking Guide

Have you always wanted to see what your processor is capable of but feared to do something wrong? Today there is an illustrated guide that will take you through the entire process, step by step. With our new guide CPU overclocking will be as easy as ABC!

by Doors4ever
10/04/2005 | 10:46 PM

We always write about overclocking: our articles, our news, our thoughts – everything is connected with overclocking. We have already published a lot of articles revealing the peculiarities and special tricks typical of overclocking different types of systems and hardware. In fact, the info you can get from these materials is more than enough to get down to overclocking for the first time. The experience will come with the time.


However, I can still very well imagine how lost a commencing overclocker can actually be when he realizes that he needs to find his way in this endless stream of information. It is great when someone with more overclocking experience is around to give you a few hints. And what if there is no one else there to help? In this case, even a simple operation like accessing the BIOS Setup may turn into a real challenge for the first-time overclocker. I continuously receive tons of e-mails with questions like “what keys shall I hit to overclock my CPU”. Well, today’s article will be specifically devoted to all these keys.

Of course, the pure “key-hitting” approach to overclocking will not bear the desired fruit. Before you press this or that key you have to understand why you are doing this and what this may lead to. And even though the potential hazards resulting from incorrect overclocking are quite significantly exaggerated, it is still quite possible to break the system down by doing something completely wrong. That is why all overclocking related articles usually start with long introductions where the authors try to mention all potential problems and remind the user of solely his responsibility.

Well, I assume our readers are all smart, reasonable people that is why I will not bore you with long introductions (which tend to be skipped most times anyway). Assume, that I have warned you.

Special Overclocking Tools

So, today it is very simple to overclock a CPU. All you need to do is increase the clock frequency of the processor core. There are different programs and utilities that allow overclocking right from the Windows. Take, for instance, ClockGen :

There are a few different versions of this utility designed for different mainboards and chipsets. Moreover, many mainboard vendors offer their own overclocking tools. For example, EasyTune5 from Gigabyte :

...or CoreCenter from MSI:

You can find these programs on driver CD discs that are bundled with the mainboards from these vendors, and the updated versions can be downloaded from the mainboard manufacturers’ web-sites. Is it good to use these utilities for overclocking purposes? Of course, it is. Sometimes, it is the only possibility to overclock the CPU if the mainboard offers very limited options for overclocking from the BIOS Setup. However, despite the seeming convenience and easiness of overclocking from these special utilities, I personally prefer not to use them if there is a choice. And there are multiple reasons for that. First of all, any program may have bugs, and do we really need any additional problems? When you overclock the CPU from the BIOS Setup, you do it immediately after the system boot-up, and the tools and utilities we have just mentioned will only start working once the Windows is running. Moreover, the system boot-up and windows loading can already be a sort of a stability test for the overclocked system. All in all, if you would like to overclock your CPU with the help of special tools and utilities, you should hardly have any serious issues ever: you can read the utility description on the manufacturer’s web-site or in the mainboard manual. So, today I suggest paying special attention to overclocking from the BIOS Setup.

Accessing BIOS Setup

How do we get there? Usually all you have to do is press the <Delete> key on the keyboard during system boot-up. You can do it multiple times, just to make sure. Don’t disregard the information that appears on the screen. Read it. Sometimes, it may also be useful to look through the mainboard manual before getting started, because sometimes there might be a different key or combination of keys assigned to let you into the BIOS Setup. Gigabyte mainboards, for instance, require the user to press <Ctrl+F1> once you get into the BIOS, otherwise, you will not be able to access any of the options there. As a result, you should see the following screen:

Don’t be confused by a lot of unknown words and terms. Even though the BIOS versions are different and some options may be called differently, we will still find everything we need just fine.

For our overclocking experiment we need to increase the CPU frequency, which is calculated as the CPU clock frequency multiplier multiplied by the bus frequency. For example, if the nominal frequency of the Intel Celeron D 310 processor is 2.13GHz, its multiplier is 16x, and the bus frequency is 133MHz (133.3 x 16 = 2133MHz). In other words, we have either to increase the multiplier or to raise the FSB bus frequency, or raise both these parameters accordingly. Contemporary Intel processors have locked clock frequency multiplier which cannot be changed (some top models allow reducing it down to 14x with the help of special power saving technologies). As for AMD CPUs, some allow doing this, I mean increasing both parameters simultaneously. However, at this point I suggest that we take a closer look at the more general case, when we overclock the CPU by increasing the bus frequency. It is especially interesting, because this way you can increase the overall system performance quite tangibly.

Why? Well, a lot of things inside a computer system are connected and synchronized with one another. For example, by raising the processor bus frequency we also increase the memory working frequency, speed up the data transfer rates and hence increase the overall system performance. However, there is another side to this picture: by overclocking both – the CPU and the memory at the same time we can exhaust the potential earlier. Very often it turns out that the CPU can be overclocked more while the memory has been pushed up to the limit. Right now only NVIDIA nForce 4 Intel Edition based mainboards allow overclocking the processor and the system memory independently. There are very few mainboards like that out there, so I assume you are very unlikely to have one. Therefore, before we get down to the actual CPU overclocking we have to make sure that our hands will not be tied up by the memory potential or something like that.

Lowering the Memory Frequency

Let’s find the corresponding BIOS option that is responsible for the memory working frequency. It can sit in various sections of the BIOS and be called differently, that is why you should better consult the mainboard manual first. This option is most often found in one of the two sections: the page devoted to memory overclocking and timing settings, or the page dealing with CPU overclocking. The first page is most likely to be called Advanced Chipset Features or simply Advanced , like by ASUS. The option we are looking for is called Memclock index value and is measured in megahertz:

It can also be located in the page called POWER BIOS Features like by EPoX and be called System Memory Frequency or simply Memory Frequency . The frequency in this case might be marked as DDR400, DDR333 or DDR266, and might be just PC133 or PC100.

It doesn’t really matter for us: all we need to do is to find this parameter and set the minimal possible value for it. There are several ways to set this value depending on the BIOS version and the mainboard manufacturer. You can either press <Enter> and select the value from the drop-down list with the keyboard arrow keys, or you can sometimes go through the values with the PageUp, PageDown, “+” or “-“ keys.

Why do we have to set the memory frequency to the minimum? I bet your memory is far not that slow and can work a way better than the minimum value we set for it. Well, during the CPU overclocking we will increase the FSB frequency. In this case the memory frequency will also grow up, however, we hope that if it starts growing up from the minimal value instead of the nominal one, it will have more room to grow. Namely, it is more likely to stay within the supported range and not to limit the CPU overclocking process. Just to make sure, you can also set the memory timings to slightly higher values than those set by default.

Firstly, it will push farther back the stability limits for our system memory. Secondly, if the timings are set automatically, the mainboard may set memory timings to extremely low non-functional values, and by doing it manually we can always make sure that the memory timings will work just fine. To see if it worked, we have to save the BIOS changes and reboot the system. To do this you have to select Save & Exit Setup option or just hit F10 key and confirm your intentions by pressing <Enter> or “Y” (Yes) in the older BIOS versions.

In most cases it is enough to set the memory working frequency to the minimum, so you can finally get down to the actual CPU overclocking. However, since we are doing it for the first time let’s not rush the things and double-check that everything has been done the right way.

Adjusting Frequencies of Other Busses

When I said that all the things in a computer system are interconnected, I didn’t mention that the memory frequency is not the only parameter that will increase together with the growing processor bus frequency. Other frequencies, such as those of PCI, Serial ATA, PCI-E or AGP busses will also get higher. It is even good to some extent, as it can also speed up the overall system performance a little bit, however, if these frequencies get a way beyond their nominal values the system may simply refuse to boot at all. Nominal frequency for the PCI bus is 33.3MHz, for the AGP bus – 66.6MHz, for the SATA and PCI Express – 100MHz. almost all contemporary chipsets know to lock these frequencies at their nominal values, however, it would be good to make sure it is really so. To do it you have to find AGP/PCI Clock parameter and make sure it is set to 66/33MHz.

All this is true for Pentium 4 Intel chipsets, for NVIDIA chipsets and the latest SiS chipsets. However, the early Intel chipsets, SiS chipsets and all VIA chipsets do not know to lock the frequencies at their nominal values. In reality it means that if your mainboard is based on VIA K8T800 chipset, for instance, you will not be able to go beyond 225MHz FSB frequency during overclocking. Even if your CPU can do better than that, you will have to stop at this point, because the system will not recognize the hard drives any more, or because the integrated sound on your mainboard stops working. Although, you can still give it a try, and later in this article we will talk about it.

The HyperTransport bus frequency is very important for NVIDIA chipsets for AMD Socket 754/939 platform. By default it is set to 1000MHz or 800MHz, and it would be better to set it to some lower value before you start your overclocking experiments. Sometimes, you may see the actual frequency written in the BIOS Setup, but in most cases you will come across 5x multiplier for 1000MHz frequency and 4x multiplier for 800MHz.

This parameter may be called HyperTransport Frequency , or HT Frequency , or LDT Frequency . You have to find it and reduce the frequency to 400 or 600MHz (2x or 3x multiplier).

So, we reduced the memory frequency and HyperTransport frequency, locked the PCI and AGP bus frequencies at their nominal values. Now we can play around with the CPU overclocking.

CPU Overclocking

FSB Frequency

To get started we need to find the Frequency/Voltage Control page…

…which may be called POWER BIOS Features by EPoX mainboards…

…or JumperFree Configuration by ASUS mainboards…

…or μGuru Utility by ABIT mainboards:

I don’t think different section names may cause us any trouble. So, once we are there we start looking for the parameter called CPU Host Frequency, or CPU/Clock, or External Clock or something similar, which is in charge of the FSB frequency. This is the parameter we are going to raise.

How greatly shall we raise it? I don’t know the answer to this question. A lot depends on your CPU, mainboard, cooling system and power supply unit. Start little by little: try raising the FSB frequency by 10MHz above the nominal – it should work just fine in most cases. Don’t forget to save the changes, load the Windows, make sure that the CPU really did overclock (you can use something like a CPU-Z utility to check this out). After that check how stable your system is by running some program (like Super PI, Prime95, S&M) or game. Of course, you have to make sure that this program runs stable on your system before you undertake any overclocking attempts. And do not forget to monitor the CPU temperature: the lower it is – the better, and make sure that it doesn’t exceed 60o C.

If you have an Intel Pentium 4 or Celeron CPU, you should use ThrottleWatch, RightMark CPU Clock Utility or something like that. The thing is that these processors could start throttling in case they get overheated thus reducing the system performance dramatically. It doesn’t make any sense to undertake any overclocking experiments in case the CPU is “throttling”, because the performance may drop even below the level achieved with the nominal settings. These utilities will report if throttling occurs, so that you could improve the CPU cooling or take it easier on overclocked settings.

If everything came out OK, you can increase the FSB frequency a little bit more until the system remains stable. Once you start noticing the first signs of over-overclocking, such as freezing, unexpected program termination, error messages, blue screens, or once the temperature grow too high, you have to get back to the lower FSB value and make sure the system remains stable in this case again.

Very often you may refer to our previous overclocking related articles to evaluate how far your CPU can approximately go. Just be attentive and keep in mind that it is not only the CPU name that matters, but also the type of the core it is based on and even the core revision. Moreover, even the CPUs from one and the same supply can have different overclocking potential, so don’t try to immediately set the maximum frequency you have even seen mentioned in relation to the same CPU: it would be much safer for you and for your system to reach these heights step by step.

However, there can also be exceptions. Remember, when I mentioned the older chipsets that cannot lock the AGP and PCI frequencies at their nominal values? It is true, they cannot support the nominal frequencies of these busses throughout the entire FSB frequency range. But they have to keep these frequencies at nominal when the CPUs work at their standard clock rates. This is done with special dividers that switch automatically depending on the FSB frequency. The standard frequencies in this case are: 100, 133, 166 and 200MHz.

Suppose that we overclocked a Duron processor from 100MHz to 120MHz on the bus and it remained absolutely stable all the time. But when we increased the FSB frequency to 125MHz, some freaky things started happening and the system would even refuse to boot at all. Of course, we could have reached the top of the CPU overclocking potential, but it could be a completely different reason. What if the CPU can go much farther than that, and it is the higher AGP and PCI bus frequencies that do not let us continue? You can check it out pretty easily: set the frequency to 133MHz. In this case the mainboard will use different dividers to set the bus frequencies to their nominal values. If your CPU copes with this overclocking, you will be able to go somewhat higher.


Shall we increase the CPU core voltage? Sometimes it might help, but not always. The CPU heats up more during overclocking anyway, and by raising the core voltage you increase the heat dissipation even more. Therefore, I wouldn’t recommend to start playing with unreasonable Vcore settings. Although, this is your system, so you are surely free to do whatever you want. Please, don’t e-mail your complaints to me then: I have just warned you. :)

Clock Frequency Multiplier

As for the CPU clock frequency multiplier, there are a few CPUs that boast an unlocked one, i.e. this multiplier can be changed. Among these CPUs are: AMD Socket A (462) processors manufactured before week 40, 2003; AMD Athlon FX: AMD Socket 754/939 (except the youngest Sempron models). By changing the CPU clock frequency multiplier your acquire more flexibility during CPU overclocking. For example, if you have an old mainboard that doesn’t allow locking the AGP and PCI bus frequencies, you can overclock your CPU by simply increasing the clock frequency multiplier. Since you do not touch the bus frequency at all, the PCI and AGP bus frequencies will stay at their nominal values.

Another situation is also possible: if your CPU has a pretty high nominal clock frequency multiplier already, you can set it to a lower value and thus offer yourself more room for bus overclocking. This way it will certainly contribute to the overall system performance improvement. Some AMD Socket A processors have a locked clock frequency multiplier, however, there are ways to unlock it or “turn” these CPUs into mobile processors, which will also allow adjusting the multiplier. I will not go into all these details this time, but we had a few articles about it in the past, so you may find them in the CPU section on our site.

Emergency Break: Clear CMOS

And what shall we do if the system is over-overclocked, if the parameters have been set incorrectly, and the mainboard doesn’t even boot-up, or system hangs shortly after booting? Some contemporary mainboards monitor the boot-up process and if something interrupts it, the mainboard restarts with the default settings for the processor and system memory. In this case, all you need to do is access the BIOS Setup and set the correct values.

Sometimes, you can cure the system by rebooting it while pressing and holding the <Ins> key. In this case the mainboard also resets all the values to the nominal that allows to boot the system successfully. If nothing helps, you have to find the Clear CMOS jumper, shut the system down, switch it to two next contacts for about three seconds and then return back to the initial position.

Now absolutely all parameters will be reset back to their nominal values. So, next time, don’t go that far.


So, the CPU has been successfully overclocked, but your work is not done yet: it is not only the CPU that makes the system performance. Have you already forgotten that you reduced the memory working frequency in the very beginning? Now you should bring it back up by setting the most optimal timings. Here you should better go for advice to your friends who may have already done it before or undertake a few experiments of your own: high frequency doesn’t always result in high performance. Adjust the parameters one by one and test all the changes you’ve made right away. If you are a gaming fan, then the next thing you might want to do will be graphics card overclocking.

Well, you know it is impossible to write everything in one single article. There are a lot of details, of course, but overclocking is not a complicated thing to do. Check out our previous articles , our Forums and talk to your friends. But before you get to overclocking, think: an unoverclocked system working stably and reliably with its nominal settings is much better than a system overclocked to the point of no return.