What is overclocking?
For the purposes of this guide, overclocking is the process of increasing the "clock speed" (FSB, multiplier, RAM timings etc) of a component in order to gain increased performance.

The Benefits
So why would you bother to overclock your PC? First and foremost, the idea that you can get more performance out of your PC without spending a cent is an attractive one to any gamer. While Counter-Strike is probably not stretching your system to the limit (anything over a PIII 800/GF2MX/128MB RAM should be fine), if you're into playing the latest games or working with multimedia applications (video encoding, 3d-rendering etc) a solid CPU and video card overclock should give noticeable performance improvements. Depending on your system (and how far you are able to overclock), in general terms, anything from a 1% to 40% increase in overall speed is possible.

Not so fast...
Before you begin you get ready to celebrate a free 40% performance increase, keep in mind that not every system is suited to overclocking. In fact, some CPU and video card combinations may only run at stock speeds—and simply won't budge any higher. While this situation is fairly rare nowadays, manufacturers aren't required to make their products overclockable—you get what you buy. Additionally, to make any kind of noticeable (and stable) CPU overclock, you're going to need adequate cooling—sometimes the standard cooling can handle higher temperatures but don't rely on this.

The next catch to this seemingly wonderful idea is that to actually make a noticeable difference to system performance, a fairly substantial overclock is required (i.e. at least ~10%). While overclocking your CPU from an AthlonXP 1600+ to a 1700+ may seem like an exciting achievement, you're going to need a stopwatch to tell the 3% difference in clock speed.

To throw the final spanner in your overclocking dream, overclocking your CPU or video card most likely voids the component's warranty. While this is not always true, generally speaking, a hardware manufacturer is not going to replace a part damaged as a result of overclocking. Why is this a problem? Simply because the increased heat generated through overclocking can damage a component—you may have heard of those "frying their CPU" and such. All that said, it's not that risky with current hardware—most motherboards now have built-in heat detection and shutdown (though you can't solely rely on this). If you're careful, and don't change any settings too dramatically, you should be able to avoid any such problems. However, be warned, overclocking can damage your hardware: you overclock at your own risk.

The front side bus or "CPU Clock" can be adjusted in the BIOS
Before I get into the detail, it should be noted that there are other things you can do to improve system performance before beginning to overclock—most important is to download the latest drivers for your hardware. Getting the latest BIOS for your motherboard is also very handy—newer versions often come with greater overclocking flexibility.

The general process of overclocking is fairly simple and is similar for both CPUs and video cards. The goal of the process is to get your component running at the highest clock speed it's capable of running at stably. To achieve this, the basic idea is to push your hardware to the limit and then bring it back a bit (to stable levels). The first step is to look around the internet to see what kind of speed others with the same components have been able to overclock up to. Check out the links section at the end of this article for some good starting points. Be warned, every component overclocks to a different amount—my AthlonXP 1700+ could be very different to yours. Despite this, any results from others that you can find should be useful in giving you a reasonable starting point.

Before you start, it's important that your CPU (and entire case) has good cooling—this means a quality CPU heatsink/fan (HSF) and good ventilation (usually case fans are required). Getting your case properly ventilated is simply a matter of fiddling with fan position and directions. As a general guide, it's a good idea to have the exhaust fan higher up on the case (to blow out the hot air that has risen inside the case) and to place the intake fan near the bottom. A cramped mini-tower with no space for a case fan and only one small ventilation grill is just going to turn your PC into an oven as soon as you start the OC process—you won't get anywhere. That considered, once the cooling is all ready, it's time to start.

BIOS Time
For clarity (and "real" numbers), I'll use my current CPU as an example. I've checked out a few forums and read around a bit and reckon I should be able to get my 1700+ (AMD AXP Thoroughbred) up to around 1.9Ghz (just above the equivalent of a 2300+). There are 2 "clocks" that you can change in the bios which affect CPU speed: the multiplier and frontside bus (FSB). These settings are accessible in the BIOS—usually in a section called "Advanced Chipset Features", "Power and Frequency Control" or something similar. The final "CPU Clock Speed" is the product of multiplying the frontside bus by the multiplier (who would have guessed?). Note: different BIOSes may label these settings differently—"multiplier" and "ratio" are the same, as are "FSB" and "CPU Clock".

Thus, to increase the final CPU clock to my goal near 1.9Ghz, I could change the CPU clock to 175 and the multiplier to 11: 175 x 11 = 1925Mhz. Unfortunately, not all BIOSes will let you change both these options: it's a matter of downloading the latest BIOS and then trying it out. Again, motherboard manufacturers aren't required to let you change these settings—they're a "feature" (though most newer chipsets do let you manipulate both these options). In reality, I would start with a lower FSB and multiplier and slowly work my way up to 11 * 175, testing each speed for stability and increasing the power settings as necessary (read on for power explanation).

Unfortunately things aren't usually that straightforward. Depending on your motherboard, CPU and RAM, matters can get a little complicated.

DDR What?
With DDR (double data rate) technology, two "cycles" (output) can be performed per clock—potentially doubling the output. This means that while you buy DDR "333" RAM, the actual MHz clock is half of this—166Mhz (a clock of 166Mhz x DDR gives an effective speed of 333Mhz). In CPUs, it's a similar story. With most current AthlonXPs, the default FSB is either 266 or 333Mhz—an actual FSB frequency of 133 or 166Mhz in DDR mode. These "DDR frequencies" are often suffixed with DDR to make things clearer (e.g. 333Mhz DDR). In the newer Pentium 4's, the FSB is the often "quad pumped"—the final FSB is 4x the CPU clock. It may all sound a bit confusing but as far as overclocking goes, you just have to know which settings to change and what effect they have.

In Synch!
Your system will generally perform better if your memory clock and CPU FSB are "in synch"—both are the exact same speed. Without getting into the detail, this synchronization allows the CPU and RAM to function more efficiently together—resulting in increased performance. For example, a PC with DDR400 (PC 3500) RAM provides better performance with an AthlonXP FSB 333Mhz DDR when the RAM is run at 333Mhz DDR to keep "in synch" with the CPU's FSB. With newer motherboards, there is often a "synch" option in the bios so you can make sure the CPU FSB frequency is locked to the RAM clock. Despite the advantages of synchronization, remember that your RAM modules may reach their clock limits long before your system/CPU has. In this case, you can sometimes get more performance by running at a higher FSB while running the memory slower (out of sync) though the RAM will bottleneck performance somewhat.

Additionally, without what's called a "PCI lock" and "AGP lock" (features only present on some newer motherboards), when you increase the CPU FSB, the PCI AGP bus are overclocked as well. This causes problems as, in most cases, the system becomes unstable (the PCI or AGP buses have reached their limit) before the CPU itself has reached its limit.

Powering Up...
As you raise the FSB and multiplier, the CPU will become increasingly unstable—either the system won't boot or it will restart if put under any pressure. To fix this, you need to increase the power supplied to the CPU—this is a setting called the Vcore. Vcore is able to be changed under a category named something like "Power Management" in your BIOS. Don't change the Vcore until you've done some reading as to how much power your CPU can take. Unfortunately, raising the Vcore also increases the temperature of the CPU—you're going to need effective cooling to keep it at stable temperatures. Just to add to the inferno now sitting in your motherboard, the CPU temperature is also constantly increased as you increment the FSB and multiplier as the CPU is being pushed to run at speeds beyond its factory settings.

Keep an eye on temperatures, fan stats and power settings
In terms of damaging your CPU through heat—if you're overclocking to reasonable levels, there shouldn't really be much danger as the system will become unstable (and hopefully shutdown) long before the CPU temp reaches dangerous levels. Instances where CPUs are "fried" usually occur as a result of a combination of bad cooling (e.g. having no thermal compound between the HSF and CPU) and a failure in the motherboard to shutdown in time. Generally speaking, Athlons are much more likely to burn out like this but Pentium CPUs can also be damaged through overheating. While this is still a very real risk, as long as you're careful and you are using a newer motherboard with built-in thermal shutdown, you should be pretty safe. (note: jumping to max Vcore and Vdimm and maxing the system clock is NOT "safe"). To keep an eye on temperatures, fan stats and power settings, it's always handy to have a hardware monitoring program running. If you're motherboard doesn't come with one, Motherboard Monitor is an excellent third party solution.

Just when you thought that your system couldn't possibly take any more heat—there are other contributing factors as well. On top of the heat coming from the CPU and RAM, the motherboard's "north-bridge" (main chipset) can also become quite hot at higher FSBs (200MHz+). Sometimes the northbridge needs its own fan to remain stable at these higher system clocks. Just to burn whatever charred remains are still in your PC, many of the different components also radiate their own heat. It's the combination of these factors which makes it very important to have effective air flow through your case—otherwise the air inside just heats up making your CPU HSF pretty useless (blowing hot air onto a hot heatsinc doesn't do much good) and adding to the overall instability of your system. Of course, all these case, CPU and motherboard fans are going to make a fair amount of noise. Turn the music up I say! Seriously though, its up to you to decide on a balanced compromise between noise and cooling. Again this will be different for everybody. Alternatively, if you have to have the best, there is always water cooling. I'm not going to go into the detail of water cooling—suffice to say that it cools very effectively (if set up properly) and is much quieter than an "air" system but a good retail setup is really going to put you out of pocket.

It should be noted that with 2 or more case fans, a large CPU fan, increased motherboard power settings and multiple hardrives or CD drives, your system is going to require a lot of power to run stably. With this kind of setup, a 300W PSU (power supply) is just not going to be up to the job. I'd recommend at least a good quality 350W PSU to keep a well cooled overclocked system running. If your PSU can't take the load, many problems can arise—system instability, failure to boot and even PSU failure.

Remember the RAM
Like your CPU, as the RAM clock is overclocked, it becomes increasingly unstable—signs of this instability are similar to that of the CPU: system crashes, restarts and failure to boot. And, like the CPU's Vcore, you can increase the power supplied to the memory through "Vdimm" to try to stabalize the overclocked RAM. But again, like Vcore, this will increase the heat involved so effective cooling is a must (a case fan blowing over the RAM modules isn't a bad idea). Apart from the RAM clock, you can also change other "timing settings" for the RAM modules. These timings are usually accessible from within the "Advanced Chipset Feature" section of the BIOS. While lower timings mean faster RAM performance (a CAS latency of 2 is faster than 2.5 etc), as you increase the RAM clock speed, you won't be able to keep the timings low. Hence, there is a tradeoff in which you have to find the performance maximum—a balance between a high RAM clock with slow timings and a lower RAM clock with faster (low) timings. Better quality RAM will be able to withstand lower timings at higher clock speeds. For example, Cosair XMS memory (one of the best) certainly has greater overclockability than lower quality RAM—though this extra performance comes at a price.

As with the other options in the BIOS, RAM timings may or may not be accessible depending on your motherboard and BIOS version.

Video Card Overclocking
Generally speaking, video cards don't usually overclock to the same extent as CPUs. Despite this, any substantial overclock you can make should greatly increase performance in 3D games. As for the process of overclocking itself: it's pretty simple for video cards. First off, make sure you get an overclocking program which works with your video card. Personally, I use PowerStrip. As with the CPU, the idea is to increase the engine and memory clock of the video card to the highest stable level (note: to access these settings in PowerStrip, simply right click the task bar icon and select Performance Profiles > Configure...). Again, to get an idea of how far your video card is going to overclock take a look around—3DMark online results often has some useful info.

Video card overclocking can be performed easily from within Windows
With most modern video cards, I've found memory overclocking seems to have the greatest impact in 3D games—though you'll just have to experiment to find the effects on your system. Signs that you are reaching unstable speeds are obvious—first, graphical glitches in 3D applications may occur and at higher levels the system will often freeze or crash. At this point, it's wise to lower the settings to a stable level—often your overclocking utility will detect this and help reset them for you. However, sometimes you may get stuck as your system freezes/crashes everytime you get into Windows. When this happens, the simplest solution is often to boot Windows into "Safe Mode" (hit F8 at start up) and to try reset any settings from there. If worst comes to worst, you should be able to uninstall the video driver from in safe mode—removing any overclocked settings.

To try and increase stability at higher speeds, you can increase the power supplied to the AGP card (just like Vcore and Vdimm) in the BIOS. However, leaving this at default power levels is a wise idea unless you're feeling confident (and your case/video card has effective cooling).

And you're off!
I hope this has been useful in giving you a solid starting point for PC overclocking.