NB: No longer updated, information may be out of date.

This guide is aimed mainly at newbies (and not been updated in a while). I can guess that most people out there are a bit worried about overclocking. This is basically going to answer pretty much every question you wan't to ask. If I don't answer it try the forum for more specific answers.

Q: Why overclock?

A: Something for free you might think? Exactly. Wouldn't you prefer to have a 600 compared to a 450 without paying any extra money? Most chips will overclock even if it's just an extra 50mhz it can give that performance increase your after.

Q: Is it illegal?

A: Overclocking is not illegal unless you sell someone an overclocked chip as something else without them knowing.

Q: Will it invalidate my warranty?

A: Overclocking does invalidate your processor warranty and in some cases where overclocking is using unorthodox bus speeds (i.e not 66,100,133) can invalidate the warranty on all the peripherals running on it, but unless there are tell-tale signs, they don't usually know.

Q: Will I fry my chip?

A: The word 'fry' says it all, if you can keep your chip at around 45c when at 100% use then it is unlikely to burn out. Heat is the overclockers enemy so the cooler the better - a cooler chip usually overclocks more or is more stable.

Q: Is it reliable?

A: Yes, and no. If you want to know if it's reliable, use the stability tester (in the downloads section). If you are worried don't overclock to it's limit, just go one notch down.

Q: Will I corrupt my harddrive?

A: If you use an unorthodox bus speed and run your PCI bus higher that 33mhz (discussed later) then there is a posibility of harddrive corruption.

Q: If overclocking is so reliable, why don't intel and other companies overclock them and make more money?

A: Because intel actually underclock, when they bring out the first processors in a range for instance the piii450, it is probably actually a remarked 600. For instance if they are still selling the 450's and they have a surplus of 600's, they will underclock the 600's and sell them on as 450's. It cost's them the same amount and in the long run it makes them more money as not everyone can afford the newer chips and they sit in the factory doing nothing. The other scenario is they make the 450 easily capable of higher speeds and as they release new products, they just increase the speed and possibly the voltage and cooling - this is basically overclocking. It's all about money at the end of the day. And finally for this scenario I will use the Celeron 533 and Celemine 533. The Celeron 533 is at the limit of the 0.25 micron process. The celemine uses the 0.18 micron process and as it is known, will relativley easily reach 800 because of the updated core. So why don't they just start selling at 800? Becaue no-one can afford an 800, so to make money they stick it down to 533 and carry on making AS MUCH MONEY AS POSSIBLE. I think you get my drift.

Q: So I get my pii 300 to reach 400 - does that mean my friends will?

A: No, each chip is different even if they are from the same batch can have dissimilar overclocking ability. The motherboard also effects the way a chip overclocks (discussed later) .

Q: So is it pot luck how overclockable my chip is?

A: Yes but if you want to, you can buy gauranteed overclocked chips from places such as www.overclockers.co.uk, www.computernerd.com and www.pcnut.com. I personally beleive buying these are what is causing AMD to lock their processors, so take the gamble and buy non pre-tested.

Q: So if I can't reach a certain speed, is it just a limitation of the CPU?

A: No, RAM can be a problem. In most cases 66mhz RAM will reach 100mhz and 100mhz RAM will reach 133mhz. Sometimes CAS3 instead of 2 helps, but occasionly they jsut can't do it. Sometimes they go further but not necessarily. Another limiting factor is when using unorthodox bus speeds, the PCI devices and AGP card can't always handle it.

Hopefully that has answered a few questions but now lets discuss it in more detail. This is how it works.

The example I am using here is a Celeron 400mhz. All intel processors are multiplier locked apart from some of the earlier chips (i've seen locking as far back as the 133). That means technically we have to overbus a celeron to get a higher speed.

Take a look at the diagram to the left. This shows how the bus speed affects the rest of the computer. If you increase the bus speed it follows the same rules, i.e the dividers. In some motherboards they can select which dividers to use but in most cases it is automatically determined by pre-defines boundries set by the motherboard or PLL chip.








The diagram to the right shows how by upping the bus speed is actually increasing the AGP and PCI bus therefore overclocking all other devices in the system. In most cases, having the PCI at 38 is all right for most devices.

At 83mhz the PCI is running at 42mhz! thats almost 30% above the recommended amount. At this speed the harddrive can corrupt (the harddrive runs through the PCI). If you do try this speed, boot into DOS first and try running the original Quake to do an initial stability check. If you are happy it is stable then try windows.










If you push your processor to the 100mhz mark then the only warranty you are voiding is the processor. Most celerons above the 400's won't do 100mhz. Celeron II's on the other hand...








Now in the case of AMD and Cyrix, they are not multiplier locked so the safest thing to do is just increase the multiplier. eg 6.5 x 66 = 433. But if your RAM and motherboard support it you could decrease your multiplier and up the bus speed eg. 200mhz AMD (66x2.5) to 100x2 increasing your RAM speed without overclocking your CPU. Cyrix chips run very hot and I wouldn't recommend to a newbie to try and overclock it.

We have so far covered a lot of theory but no practical. How do you overclock your computer? It all depends on your motherboard and type of processor. Basically to overclock any CPU, tell it it's something it's not. In order to do this you need to somehow instruct the motherboard that what is in your computer is a different processor. Here is my step by step guide to overclocking intel processors. AMD and Cyrix come later.

Intel Processors

Get your motherboard manual out. Look at the processor upgrade section. There are three types of motherboard processor selection.

If you have to change the jumpers on the motherboard you need to find the BUS SPEED section in your manual. Set the bus speed to one jump up from the original bus speed. When it boots it should tell you the processor speed (else use your head, bus speed * multiplier = CPU speed). Then run my test for stability routine (at the end of the document). When you are happy it is stable, try a higher speed. If a speed is not stable or you can't reach a speed try upping the voltage by 0.1volts. My general advice is not to go more that 15% above the default voltage. Another reason for instability is cooling. Read my cooling FAQ for tips on this.

If you have to select the mode in the BIOS, life couldn't be easier. Goto the CPU speed menu and select 'user define'. From there follow the same steps as above. You may have to deselect some sort of processor warning if you get an error such as "processor unworkable".

If you have a motherboard that detects the processor automatically you have two options. The first option in the case of the earlier pii's or if you are using a slotket with a celeron is to tape pin B21 to enabled 100mhz. If your processor or chipset won't go this high then the second option is your only choice. The pin taping article can be found here. I personally think the second option is the best. The second option is to use a program called SoftFSB which enables you to change the FSB from the comfort of windows. The is good because you can run your processor at its original speed when doing word processing and then increase the speed for gaming without restarting the computer! The only downside is, your motherboard probably won't have voltage settings so you won't be able to reach the speeds you would on other motherboards.

AMD and Cyrix Processors

The process is much the same as intel apart from these things, the K6, K6-2, K6-3 and Cyrix processors are not multiplier locked so unless you want to you can leave the bus speeds alone and just increase the multiplier. I do not recommend overclocking Cyrix chips to a newbie as they overheat very easily and enough to actually fry in some cases.

The Original Athlon on the otherhand is a different kettle of fish. The Athlon is very overclockable BUT you either need to crack open the case and do a lot of soldering(not recommended, not worth it) or buy an add-on card to be able to overclock. www.computernerd.com sell there Gold-Finger card there and www.overclockers.co.uk sell the freespeed card.

Thunderbirds/Durons - very overclockable. To overclock these there are two requirments. 1 - multiplier adjustment via the motherboard. 2 - A multiplier unlocked chip. Some chips may already be unlocked, but some are not and require the L1 bridges connecting - HERE

My Stability Testing Routine

The last thing you want to do is currupt your harddrive and it to be unrecoverable, so BACK UP!

Conclusion

Be careful and sensible, don't crank the voltage up too much unless you have the cooling to counteract the extra heat. Good cooling is essential so read my cooling FAQ.

Spode