Once officially frowned upon, overclocking is now very much an accepted way of getting more performance out of hardware, and especially getting more bang-per-buck by using cheap mid-range components and upping their frequency to match or exceed the level of high-end parts. Certain processors and hardware are better than others, and some become legendary. Probably the best example in recent years has been Intel's quad-core Q6600 processor, which can often easily be taken to 3GHz and beyond, even though its rated speed is only 2.4GHz. In fact, the advent of Intel's Core and Core 2 processors heralded a new era of easy overclocking. The 45nm parts run so cool in general use that overheating is hardly a problem at all, meaning you can continue to use a stock heatsink while pushing the processor way beyond its rated speeds.
For overclocking your existing hardware on a zero budget, the ideal platform is a clock-unlocked processor. This means one that allows its clock multiplier to be altered via the PC's BIOS. The basic front-side bus clock signal - the signal that allows the motherboard and its components to work together - is generated by the motherboard. That signal is multiplied so that the processor can run at its much higher frequencies, while remaining in sync with the rest of the system. A clock-unlocked processor allows this multiplier ratio to be set in the BIOS, whereas clock-locked versions can only be indirectly overclocked by upping the front-side bus speed.
The essential technique for overclocking is simple, but time-consuming. It's essentially an iterative process: boot into the BIOS and increase front-side bus or CPU multiplier frequency (or both) a little, test for stability; increase a little more; test for stability, and so on. At some point, clock speeds will get too high and the system will become unstable.
The potentially frustrating part is that this can manifest itself in a number of ways. The system may completely refuse to POST: in other words, the power-on self-test will fail and you won't even get to the BIOS start-up screen or the "happy beep" that indicates a healthy PC powering up. But it may get halfway through booting Windows and then crash with a "Blue Screen of Death" error message, or simply stop responding and just hang. If you do manage to boot into Windows, you still aren't out of the woods. The PC may seem fine, but as soon as you stress the processor the extra power dissipated by the faster clock frequency can mean the processor overheats, or you'll get random software errors, an unexpected reboot, a system hang, or various combinations of all three.
You should only deem an overclock successful once you've soak-tested the PC in its new configuration by running a CPU-intensive application for at least a few hours. The traditional tool for the soak test, believe it or not, is an old Windows 95 application called Prime95. It was originally written to look for Mersenne primes, which are special-case prime numbers. Download it from
www.mersenne.org/freesoft.
Once you've downloaded the software, just run the prime95.exe file and you'll find a helpful dialog box with a button labelled Just Stress Testing. Selecting "In-place large FFTs" will give the CPU the maximum stress, which is what we want. In the "Number of torture test threads to run" box, enter the number of cores in your CPU; in other words, enter "2" for a dual-core CPU and "4" for a quad-core. Hit OK and wander off and do something else for an hour - your PC won't really be usable, because every core will be saturated by the Prime95 routines. If the machine is still working when you get back after an hour, you can consider the overclocked state to be a stable one.
Once you push to clock settings that are on the cusp of stability, you can take things a step further and try tweaking the voltage settings to wring an even higher frequency out of the system - most motherboards allow you to adjust both processor and memory voltages. Overclocking and overvolting go hand in hand: when transistors are driven harder with a higher voltage they can run at increased frequency. But be warned that overvolting can cause problems as well as solve them.
The total power dissipated as heat increases with the square of the voltage applied to a transistor. That means a seemingly small increase of a few tenths of a volt can greatly increase the power dissipation - and thus heat - your heatsink has to cope with. It may make the transistors in the processor switch more reliably at first, but if the heatsink can't cope with the extra power dissipation it will quickly overheat and automatically go into thermal shutdown - the whole PC will simply switch itself off to protect the CPU from permanent damage. Overvolting memory isn't recommended, as it doesn't have the same overheating protection.
You should check in the BIOS to see what your options are with regard to thermal control, both with the speed of your CPU heatsink and case fans. The vast majority of modern motherboards give you the option to manually fix fan speeds at a given level, or to allow the BIOS to control them according to system temperature. For the best overclocking potential, you want your fans to be shifting as much heat away from the system as possible.
A great utility to monitor both your fans and system temperatures during and after an overclock is SpeedFan, which you can get for free at
www.almico.com/speedfan.php. It doesn't work with all motherboards, but if yours is supported you can make it control your fans, and its icon will sit in the System Tray and display the temperature readings of your hardware as reported by its onboard temperature sensors.
If you manage to overclock the PC to the extent that it won't boot at all, don't panic immediately. Recent motherboards can detect when they've failed to boot a few times in succession and automatically reset the BIOS to its fail-safe defaults. If that doesn't happen after a couple of attempts, all motherboards have the facility to reset the BIOS manually, usually by physically moving a jumper link on the board, or removing the CMOS backup battery.
Remember to go in small increments when you're overclocking. It also pays to write down the settings you're using as you go along, because you'll lose them all when you inevitably need to reset the BIOS.
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