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Advanced users

Overclocking is great & safe for advanced users

• Caution is the keyword

The principles

• Overheating is common, sometimes fatal.

Adequate Cooling is imperative.

Cooling Software is a partial solution.


CAUTION:   If you overclock, you do so entirely at your own risk.

The correct implementation of overclocking is bit complex for many users. It carries a definite risk of damage, perhaps permanently, to computer components. The possible loss of all data must also be a considered.

Ideally overclocking should be used only as a last resort when the system is on its last days, and a firm decision has been made to replace most, if not all, of that system.

This section is included because overclocking is of great interest to many users, and this site would be incomplete if the subject were not addressed.

Overclocking should only be implemented by very EXPERIENCED, ADVANCED, and COMPETENT computer users who are fully understand hardware matters.

Before overclocking a CPU it is vital that you ensure adequate cooling and that you do not have a chip already overclocked by an unscrupulous vendor!

Overclocking is the process whereby a user increases the operating speed of a component(s) beyond that recommended by the manufacturer (or by the component assembler). In common usage the term now embraces the CPU, motherboard BUS, main memory (RAM), video card, BIOS - basically any item whose speed can be increased beyond its official manufactured rating. The term 'tweak' is also used for some components e.g. 'tweak' the memory timings or 'tweak' the BIOS.

Yes! Overclocking does work - the CPU, memory, motherboard BUS, BIOS, and even some video cards. It can also, for some users, be very productive when correctly implemented However, please ensure you pay heed to the cautions on this page.

Electrical items do not operate at only one highly-specific electrical voltage or speed. They can operate, safely, within a certain (small) range. At the higher end of that range they will operate at greater speed (and also produce greater heat). Beyond that range they may still operate, but probably only for a while because of the production of excessive heat and electrical degradation - they will simply "burn out", immediately or over a indeterminable period of time.

Many computer components are not purpose-built for one specific speed; there is a ongoing process of development and a range of speeds is available - sometimes the top speed can be use safely, sometimes not. Much depends on the quality of production at the time of manufacture as well as the stage of development.

Motherboards are designed to accept a large range of CPUs. Therefore just a few easy changes to the motherboard will increase the speed of the CPU (read cautions).

The speed of the motherboard itself (its BUS) affects the speed of other components attached to it. So increasing the BUS speed also increases the operating speed of these (memory, PCI devices including video, etc.).

You may be told to run a component, especially a CPU, at a certain speed when it can safely be run at a higher speed e.g. a Pentium 150MHz is in reality a Pentium 166MHz, and many Pentium 166s can run safely (with additional cooling) at 200MHz. Likewise for some Pentium Pros and PentiumIIs.

Even your memory (irrespective of type) has a range of speeds. Many vendors set these (especially the Wait times) on the low side. The settings are accessed via BIOS.

The computer component you receive may be the early stage of the next generation but has some of its functions disabled (or you are not informed of how to enable them).

Component manufacturers make speed recommendations based on stability, reliability, and a certain life expectancy of their products. These recommendations can be excessively conservative.

Typically most CPUs can be run, safely, at least 10% faster, and some more than that (with heat precautions). The best processor Overclocking consists of a moderate CPU speed increase combined with an increase in the BUS speed.

Motherboard BUS (and hence the memory and PCI devices attached to it) can usually run faster, and usually without any problems. Remember increasing the BUS speed will also increase the CPU speed unless you reduce the Clock rate.

Memory timings are often accessible via the BIOS and easily changed. If not, then a third-party utility may be available.

Some video card settings can be altered for increased speed, and some have undocumented settings.

We all identify computers by the CPU speed - this image is the result of marketing and is not accurate. There are many other factors involved, like L2 cache, RAM, and video.

For instance a PentiumII 333 combined with a poor video card will probably perform less well than a low-speed PeniumII with a good video card - it is all about having a system with properly balanced components. Computers should be, but are not yet, judged by the operating speed of the entire system.

Obviously a fast CPU is an important ingredient in a fast system. However overall speed also depends on the settings/quality/quantity (and hence the speed) of the memory, motherboard (the BUS), chipsets, video, hard disk, and others.

Having read all of this page, you need to study your motherboard manual (or visit the manufacturer's Web site) to understand the Jumper settings for that motherboard. Then open the computer case (ensure it is earthed) and just identify the appropriate Jumpers and their possible settings. Close the case again without making any alterations. Now spend some time deciding on whether you
(a) really need to overclock
(b) are prepared to accept the possibility of disaster
(c) have enough information to firstly reduce the CPU speed
(d) have important data files backed up.
Attempting to make very large changes to the CPU speed is a recipe for disaster. To move from 90MHz to 166MHz is likely to fry your chip. It would be much safer to go from 90 to 113MHz if you can set the bus speed to 75 - this will give much improved performance, and minimize the risk of damage to the chip.

If you can manage to tweak your memory's timings as well you will get the best performance - sometimes its necessary. SDRam is especially suitable for overclocking, but many users find that EDO and FPM RAM also work.

Many of the Pentium 133MHz chips will not accept a higher multiplier; you can use only the Bus increase with these. Intel is now preventing an increase in the multiplier (clock) being recognised by the CPU in newer PentiumII & III chips. This is a de facto recognition that overclocking works, and is employed, for financial gain, by some vendors!

The only way to find out if Overclocking will be successful on your system is to try it yourself, or contact others who have done so with similar systems. Be sure you start slowly and carefully - first reduce the CPU speed via the multiplier (yes, reduce it to its lowest setting). Then, if possible, increase the bus speed, and test your system for a period. Finally increase the CPU speed to normal and then, if all is satisfactory, increase it a little.


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Don't ever forget this: All electrical items produce heat. Increasing their operational speed produces even more heat. Delicate items can malfunction with increased heat - they can even be melted by excessive heat. So be warned, and be cautious!

If overclocking the CPU then get a fan across the CPU, and a large heat sink stuck to it - the sink MUST be stuck to the CPU with a heat-conducting adhesive to improve heat transfer. You can purchase a fan and heat-sink combination, and correct advesive, at little cost.

If overclocking the motherboard (BUS) and/or the video card, then you may need to increase the cool air circulating in that area.


And, as in all computer matters, BACKUP FIRST to safe media.

The topic of heat/overheating will be mentioned many times on this page

If you allow your CPU to overheat then:

The system could become unstable giving strange errors. It could freeze, and could even cause some data to become corrupted. If you insist going too far then you may lose all data and your CPU may be destroyed.

You may, over time, shorten the life of the chip (electro migration) - it is highly likely you will have voluntarily replaced the chip & system long before this becomes a factor.

A general guideline is that the CPU is too hot if you cannot touch it for about 10 seconds without pain. Avoiding this normally requires a moderate degree of overclocking combined with the use of an additional CPU cooling fan, plus a heatsink stuck to the CPU with a heat-conducting compound.

A non-scientific guideline:

If a cold overclocked system boots and runs normally, but develops problem(s) only after a period of use, then overheating is the likely cause of the problem - so cool it down properly, or you will have to reduce your settings.

If a cold overclocked system fails to bootup correctly, then it is likely your CPU and/or peripherals will not accept the changes you made - try lower settings, and reboot.

Overclocking is actually quite safe but only in safe and cautious hands.

Having read through a pile of severe cautions, it is time to OVERCLOCK

First, a quick look at free cooling software that will help a little, and some site links that extol the ease and benefits of overclocking.

And then to the overclocking .....

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Software utilities, run but not fully tested by this site, are Waterfall and CPUIdle. Either of these offers partial protection against CPU overheating.

The CPU is not normally in use all the time; it has idle times. Operating systems like WindowsNT and Linux activate a HLT instruction during idle periods to reduce CPU activity only at those times. Less activity will mean less heat creation, a major deterrent to overclocking. They act without reducing the overall CPU speed.

This function has been available, but never implemented, in Windows 95/98. The utility enables the instruction in both. It will, for example, reduce the CPU temperature from 62 to 53 degrees centigrade (not verified) during the idle phase in a Pentium 166MHz. They are worthy of investigating though you would be advised to also use additional cooling.

It is very important to remember that heat created as a result of intense CPU activity is NOT alleviated by these utilities.
Waterfall (freeware, 117K, zip)
CPUIdle (freeware, 223K, zip)

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Tom's Hardware Guide is highly informative about all matters relating to overclocking and is well worth a visit.


THPC comment: It is extraordinary that the question of morals has been raised in relation to overclocking. There are no public moral issues involved. Your chip may 'fry in Hell' through inadequate caution on your part, but that is not of public moral consequence. You have an inherent right to enhance, use, or abuse, your own computer if you so wish.

Just be cautious. Don't get greedy!

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Please remember that you alone are responsible for the consequences of any changes you make to your computer hardware or software.

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