Guerrilla Overclocking Primer by Alan M Johnson

Why Overclock?

How would you like a PC 30 percent or more faster, for FREE, and with very little risk? It's a bit of a no-brainer really isn't it? We all know that at some point in the future we will have to upgrade our PC and this is usually to resolve a performance related issue. It's too slow, it stutters and freezes or it's simply so slow its unusable with the new versions of Windows, games or applications software.

Overclocking is becoming more popular than ever as a means of getting more out of your PC without having to spend any money. With economic times as they are this is very compelling. There are just a few good vendors and system builders out there able to offer overclocked systems that are reliable and stable so shop around if you intend on buying.

What is "Guerrilla Overclocking"?

Guerrilla Overclocking is a method that balances time required to achieve a given overclock against the benefits. One search of the internet or browse of the overclocking forums will reveal pages and pages of overclocking material that is hugely time consuming, full of omissions and errors and assumes a lot of prior knowledge and experience. The complete process and method used to produce professional PC's encompasses:

Hardware design,
Overclocking Techniques and Procedures,
Monitoring and Alerting,
Database Logging and Reporting (1000's of component combinations tested and verfiied),
Operating System Configuration,
and finally Stress and Soak testing.

Im not going to go into the full method in this hands-on practical Primer we are just going to cover enough to get you quick results so that you can go solo with your own overclocking by the time you have reached the end of the very few pages of this article. You could consider it a method for the time poor overclocker not only does it not take long to learn it also takes only a few minutes to implement in practice. Though don't misunderstand us overclocking is very complex and it's as much of an art as a science and the complexity and challenge of extreme overclocking should not be underestimated. What we are trying to give you here is a significant boost in performance with a few simple measures and without all the complexity.

Isn't it risky?

I have been overclocking memory, graphics, processors and motherboards now for over ten years and have not had one single production failure that occurred as a consequence of overclocking. I've had many failures in the lab but then that's what the research lab is for! The secret is in testing many configuration options and running many benchmarks to work out were the safe limits are and there really is quite a long way to go before you reach anything like a danger point in overclocking the hardware. There's a lot of headroom built into the quality end of the technology to cope with widely varying circumstances in which it may end up working. For example it's quite typical for a current Intel Core 2 Quad processor with a 2.66GHz factory set clock speed to run in excess of 3.5GHz with no adverse consequences.

Overclockers Mission Control

There are all kinds of tools out there from different vendors that will overclock for you, our advice is leave them on the DVD and don't bother installing them. They tend to make dynamic performance changes based on assumptions, monitoring data and utilisation and can lead to confusing stability problems or artificial performance ceilings. They also tend to "soft overclock" your PC in that unless the tool is running in your instance of windows then there is no overclock in effect at all.

The only tool you really need is your BIOS and your BIOS helps you better understand what is going on. The great thing about the BIOS is it's really, really simple and it does what you tell it. It isn't big enough to have much intelligence it's really just a heap of data that tells your PC how to run in a way that will make it work as you expect it to.

There are lots of complex settings in your BIOS and some are even important, many just aren't. I'm going to introduce you to just a few key ones you need to know about and that make the biggest difference.

The Clocks

More clock speed generally makes for more performance as the processor has more cycles per second in which to do the same task, so it does it quicker. The clocks also refer to memory and interface bus speeds as well as the processor. We will aim for the highest common possible clock speed. You will normally find these settings on an advanced page sometimes called Advanced, Tweaker, Overclock or Guru settings. The table below shows you typical high settings for 1333 and 1600 FSB motherboards and CPU's (or typical upper and lower limits).

External Clock (or Reference Clock) from 333 (fsb 1333) to 400 (fsb 1600)
CPU Multiplier (locked and not user configurable for all but Extreme or Black Edition CPU's) usually 8 or 9, can be set up to 10 as a safe upper limit
CPU Clock 2.66 to 3.2GHz, can be safely pushed to around 3.6GHz
Memory Clock, DDR2 800 to 1066MHz, DDR3 1333 to 1600MHz

The FSB speed is 4x the External clock, and the CPU speed is = Multiplier x External Clock (i.e. Clock = 2.66GHz = 8 x 333 and FSB = 1333MHz = 4 x 333). Also note on all but Intel Extreme and AMD Black Edition processors the multiplier cannot be changed and is "locked". Simple isn't it!

Now if you own a good quality branded PC or Motherboard with an Intel or nVidia chipset produced in the last three years your PC will be capable of the speeds above and more. With an nForce 780i or Intel P35/X38 chipset or later you will easily exceed an FSB speed of 1600MHz.

In my experience tweaking the memory speeds is far less significant to overall performance and if you really are time poor just leave this at the default settings. The thing to watch out for is that by default when you come to increase your FSB speed you will increase memory speed as they are linked and it's highly likely your memory will stop working well before you reach FSB or processor limits. So remember to manually "lock" memory speeds to their default working speed and latencies, usually 800MHz or 1066MHz for the former, Auto for the latter. Each time you increase your FSB you may need to recheck that you haven't inadvertently increased memory speeds.

The Volts

If the electrical power to your PC (in volts and amps) had no effect on the clock speed we wouldn't care about voltage, but it does. Like us human beings, the more work your processor does the more food (in volts and amps) it needs to keep it going. So we have to carefully feed it more volts, in doing so it draws more amps (remember ohms law; more volts == more amps!). Here in lies the nub of overclocking and what differentiates a good fast one from a poor slow one.

If we increase the voltage and therefore increase the current flowing (in amps) the resistance of all the circuitry involved dissipates some of this increased energy in heat. The resulting heat increases the resistance of the conductors and we enter a potentially vicious cycle where more heat creates more resistance which creates more heat etc. This cycle is known as thermal and or current runaway. It's conceivable that adding more voltage increases resistance and actually reduces overclocking headroom and we have observed this phenomenon empirically. So don't unnecessarily increase your voltages we want them to be as low as we can get away with.

The kinds of increases we are going to make in this exercise are in the millivolts range. The wires inside integrated circuits are finer than a human hair, a lot finer, so we have to make tiny changes or they will burn up, or resistance will go sky high and they will cease to function. That lump of copper on top of your CPU (known as the IHS, or Integrated Heat Spreader) can heat up to 70C and beyond. Now imagine how hot the insides of your CPU that are finer than a human hair need to be to be able to raise the temperature of several grams of copper that much! Now we've scared you to death about increasing voltage stop worrying about it because the table below gives you safe working voltage limits that keep you well inside a safe range.

CPU volts (VCore) 1.2V to 1.4V
Memory volts (VDIMM) DDR2 1.8V to 2.0V, DDR3 1.5V to 1.66V
MCH Core volts 1.2V to 1.4V
CPU VTT (FSB Termination) volts 1.2V to 1.4V
Northbridge 1.25V to 1.45V

Other settings

There are a few other settings below that you can optionally change however they should only be required for fine tuning an overclock near the limits of stability and practicality.

CPU C1E, Enabled, Reduces CPU power consumption and heat with an enhanced idle state
CPU TM, Enabled, Thermal protection, throttles the CPU if overheated, can confuse you while testing your overclock
CPU Execute Disable bit, Enabled, Aids virus protection by protecting code execution in sensitive memory pages
CPU Virtualisation, Enabled, Virtualisation layer support
CPU HyperThreading, Enabled, Increases CPU utilisation with effectively a second virtual core per core, supporting an additional execution thread
CPU Intel Speed Step (EIST), Enabled, Will throttle CPU voltage and speed according to utilisation, can confuse overclock results
PCIe Clock, 100, Can usually be increased by at least 5 percent and boost PCI bus speed
Spread Spectrum, Enabled, Disabling spread spectrum usually enhances stability
SATA Configuration, Enhanced, Usually this defaults to IDE or Enhanced IDE mode which is slow. Change it to AHCI or RAID mode which supports NCQ and up to 300MB/s transfer speeds. You will need to have the appropriate drivers installed in Windows first (or on first installation). Vista usually supports AHCI by default.

Boosting PC performance in six steps

Ok now you know all about the basics of overclocking and the limits around which you are working I can now give you our one minute and simple six step process to boosting your PC's performance:

1. Get into your BIOS and go straight to the page of settings for the Bus speeds and CPU settings

2. Set your BIOS Bus speed and CPU settings to manual which should open up a range of the settings described above, and we will adjust in the next steps

3. Set your CPU VCore voltage to 1.4V

4. Set your CPU VTT (FSB Termination) to 1.3V

5. Make sure your RAM speed is manually set within its limits (usually between 800 and 1066MHz DDR2 or 1333MHz DDR3)

6. The next step depends on the type of CPU you have:

6a. For 1333FSB CPU's (multiplier locked):

6a) i. Set your external clock to 400MHz, or, your FSB to 1600MHz, whichever is available in your BIOS

6a) ii. Giving you a new processor speed of up to 3.6GHz

6b. For 1600FSB CPU's (Extreme multiplier unlocked):

6b) i. Leave your external clock at 400MHz

6b) ii. Increase your multiplier to 9, giving you a new processor speed of 3.6GHz

7. Save your BIOS settings and Reboot your PC and enjoy up to a 30 percent performance boost

This works just as described with 95 percent of the systems I come across. If it doesn't work for you simply leave the voltages as described and drop the External clock, Multiplier or FSB speeds back to the default and increase them slowly a step at a time until you reach a point at which you system becomes unstable, then drop it back again. This is more reminiscent of the typical overclocking process described elsewhere. It's an iterative process that stops when you find the edge of stability and go beyond it but this way of doing it is considerably more time consuming.

Arghhhh, My PC has frozen is it broken!?

If you have stuck to this primer and the guidance on voltages above your PC WILL NOT be broken. In fact changing the clock speeds alone is highly unlikely to do any damage whatsoever. I have never seen an instance where this has caused damage even in the labs under destructive testing conditions. Heat kills, and Voltage increases current which increased heat! So be very careful when increasing your voltages and if you aren't experienced at overclocking don't go over what I recommend above.

Now my PC won't boot

If you make some changes to the BIOS and your PC wont boot, all is not lost. Most modern motherboards have what's commonly called a Crash Free BIOS or something similar. In these instances a hard power off or simply another soft reboot will put you back to your BIOS screen with the default factory BIOS settings temporarily loaded so that you can change your overclock settings. Simply reduce your overclock as described above or start back at the default settings and gradually change things rebooting each time until you find what is causing the instability.

If you don't have a crash free BIOS or it isn't doing the job then you will need to clear your BIOS CMOS memory. Reference your motherboard manual for instructions on how to do this (it's usually as simple as a button or a jumper setting). Alternatively simply remove the CMOS battery on your motherboard and this will achieve the same thing.

Important Assumptions

I make a number of assumptions about the hardware setup of your PC in order for you to get the full benefit of this primer:

You have a good intermediate level understanding of PC hardware, software and operating systems
You are comfortable getting into the PC BIOS and changing settings
You are comfortable changing the Configuration of your OS
I don't cover overclocking your graphics but we do recommend you do so as it could be the component holding you back, the same goes for your memory
Your PC has adequate cooling and good quality components installed


When you consider that a new PC three years ago is now about 20-30 percent slower than the latest PC today you can see that doing this now to a three year old PC gets you a PC at current levels of performance at no extra cost. It's hardly a trivial exercise and it's not for the faint hearted or inexperienced but once you have grasped the basics it's surprisingly simple to do and you get very worthwhile results.

Alternatively buy your next PC from someone like us and we do all this and more for you and warranty it on top. What's more you get a PC that will be two to three years ahead of the competition from the point of purchase. In industry terms this gives you almost 100 percent longer to get back your return on investment essentially halving the price of the PC.

Disclaimer: Cryo Performance Computing UK accept no liability for any consequences implied or explicit in connection with using this primer.

Alan is Chief Technologist at Cryo Performance Computers in the UK. He leads the research and development of innovative PC design for games and demanding professional communities. Cryo PC supply high performance specialist PC's. [ Cryo PC is no more].

Message from Bucaro TecHelp Webmaster: I don't recommend overclocking your PC. As many of you may know if you checked this Web site's About page, I'm a former Electronics Engineer who designed microprocessor controlled products at Motorola and other companies. Before you think about overclocking your PC, you might want to study "manufacturing process control", "process variation", and "process capability".

To put it in simple terms, the maximum operating speed of semiconductor chips coming from a manufacturing process varies, the range of the variation depends upon the process capability. Some of the chips produced will be capable of operation at higher frequencies than the specification. Most of the chips will only be able to operate at the specification frequency. Some of the chips produced will not be able to operate at the specification frequency, these are the rejects.

If most of the chips produced by a manufacturing process were capable of operation at higher frequencies than the specification, the manufacturer would raise the specification and charge more for the chips. In other words, odds are very good that your PC's chips are operating at close to their maximum frequency and overclocking them will cause your computer to produce errors.

Still, there are many PC gamer/hackers that just need to force their PC's to work faster and the chip manufacturer's, wanting to capture this market, often provide provisions to, and information about how to overclock their chips. I don't recommend overclocking, and I don't usually publish articles about overclocking. But Mr. Alan M Johnson's article is an outstanding article on the subject, and it does contain the proper disclaimer, so here it is.

Learn more at

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