Increasing the speed of your CPU, normally by increasing the FSB (front side bus) speed or the CPU multiplier.  You can also overclock your graphics card  and I dare say various other bits of your system that I haven't found out about yet!

Why do we do it?

Something for nothing!  Pushing your chip beyond what the manufacturer says it can do.  Gives you a performance boost but at the price of invalidating any warranty you have.  You'll have a high speed chip at a low price.  

But be aware that if you really mess it up you could end up losing data, or even damaging your hardware (and that's not a good thing...)

How do I overclock?

The speed of your processor is governed by the multiplier and the FSB.  Celeron processors run on a 66MHz FSB, and then Intel set the multiplier as necessary to produce the required speed.

For example a Celeron 466 runs on a 66MHz FSB, and so it's multiplier must be 7.  Simple really.

So if you could increase the multiplier you'd have a faster chip, right?  Absolutely - unfortunately Intel were none too keen on you getting more than you'd paid them for, so they locked the multipliers.  What they can't do anything about is the Front Side Bus speed of your PC, and this is where life can begin to get interesting....

In exactly the same way that increasing the multiplier will speed up your chip, so will upping the FSB.  This can be done by getting into the BIOS and simply entering the new speed you want.  However nothing in life is ever that easy is it?  A little background....

The earlier Celeron processors were based on the Mendocino core (0.25 die), and are available at clock speeds of between 300 and 566MHz.  The different speeds were attained by using different multipliers as described above, since all the chips employed a 66MHz FSB.  Why no higher than 566MHz, I hear you ask?  Well all systems have their limit, and with the Mendocino Celerons on standard cooling (more about that later), that limit is reached at around 600MHz.  Since Intel didn't want to sell CPUs that were right on their limits they only market chips up to 566MHz (mind you this hasn't stopped then releasing the 1.13 Gig Pentium III, but that's another story).

So a 300MHz Mendocino Celeron uses a 4.5 multiplier, whilst at the other end of the scale a 566 uses an 8.5 multiplier.

Back to changing the FSB.  You've entered the BIOS and reset your FSB to 100MHz.  Save the changes, reboot, and presto.  Nothing happens, your PC won't boot (if it does I'd really like to hear about it!)  Your 566 Celeron with it's 8.5 multiplier is trying gamely to run at 850MHz - very nice in theory but about as likely as Great Britain topping the medal table at the next Olympics.

Try the same trick with your 300 Celeron - unless you're unlucky enough to have a bad chip (and there are a few, but fortunately some enthusiasts with a lot more technical know-how than me have managed to identify the batch numbers of most of the Monday morning CPUs), your Celeron should happily purr away at 450MHZ, since you're still well inside it's 600MHz limit.

And so the best Celerons for overclocking are those sold at lower clock speeds, since they have lower fixed multipliers.  Historically the best of all were probably the 366s, which would virtually all run at 550.  I'm using a pair of 466s in the system this site is produced from, and they're running solid as rocks at 595MHz (you can find out more about dual CPU set-ups here).  Sadly these chips are becoming harder and harder to come by in the UK.

If you're a bit of a maths whizz you may have figured out that my Celerons are running on an 85MHz FSB.  This is where another potential snag rears it's ugly head, because not all motherboards will support the range of FSB settings you want.  For example some will only let you set either 66 or 100MHz.  What you need is a board that lets you increase the FSB in nice small increments (thank you Abit for the BP6).  If your board can't do this then you're limited in the CPU options you can use.  And of course other hardware in your PC is reliant on the FSB too, such as the PCI and AGP buses.  Some devices have quite fine limits on the FSB variations they'll tolerate, and you may well find yourself overstepping these marks in the quest for the fastest Celeron in town.

AMD processors are a somewhat different story.  Athlons and Durons are generally not multiplier locked, and even if they are unlocking them is normally a simple process which you can do with a pencil!  Overclocking your chip by increasing the multiplier is a better option in most cases than upping the FSB, because the FSB governs not only CPU speed, but also the speed that your motherboard is running at, and consequently everything else that's attached to it.  This means that if you bump up the FSB to run your CPU faster you are also increasing the speed of your RAM, hard drives, PCI and AGP buses.  Now this may give you an even greater gain in performance, but just as your CPU has limits so do all these other components.  

Certain hard drives and graphics cards (both PCI and AGP) are quite sensitive to changes in bus speed.  If your RAM won't support the new FSB (e.g. you're trying to run PC100 RAM at a 133MHz FSB), you're in a creek without paddles situation.  If your hard drive doesn't like the new speed you may lose data or damage sectors on the drive, both of which are bad news.  And if your 3D card isn't happy then video performance is going to suffer.  

The PCI/AGP buses are normally set by your BIOS to run at a fixed fraction of the FSB.  For example, the PCI and AGP buses run at around 33MHz and 66MHz respectively, so in a Celeron system designed to run on a 66MHz FSB the buses are set at 1/2 and 1/1.  Therefore if you manage to overclock your Celerons to run on 100MHz FSB you are also overclocking the PCI bus, now running at 50MHz, and the AGP bus, now running at 100MHz.  Depending on what cards you are using this may give you problems; fortunately all is not lost, since some makes of BIOS will permit you to alter the fraction of FSB that the PCI/AGP buses run at - the Abit BP6 has Award BIOS which will let you alter the settings for both buses - nice!  The bottom line is to talk to other people using similar components before you try any radical changes to the FSB if you have any doubts.  However ff you can change the multiplier you are, quite literally, laughing.  This will affect the speed pf your CPU and nothing else - RAM, hard drives and expansion cards are all untouched.  Which is probably why Intel locked all the multipliers in the first place....

Another variable you may need to look at is the voltage being fed to the CPUs.  A decent motherboard will again allow you some flexibility here, a slight increase in voltage may be needed to get your chip to run at it's new clock speed.  For example my Celerons are now using 2.10 volts rather than the stock 2.00 volts.

Provided you've got hold of some Celerons at the right sort of clock speed, you've got a motherboard with some  built in flexibility, and your PCI and AGP cards stay in spec, you should be ready for some overclocking.  But don't leap straight from the 66 to the 100MHz bus - build up in small steps giving the system plenty of time to stabilise in between adjustments (by plenty of time I'm talking days, and if possible leave the system running at all times).  If all seems well try tweaking things a little further; after a time you'll reach the point where your system cries "Enough!"

Well it won't say that in fact.  Actually it probably won't do anything at all, just present you with the dreaded Blue Screen Of Death.  Don't worry, your PC isn't dead - well probably not.  Restart it, get back into the BIOS, and adjust the FSB back to the last known good setting.  I did tell you to make a note of the settings, didn't I?

Well overclocking is a massive topic and I've really only scraped the surface there, but hopefully that's enough to whet your appetite.  You can find answers to most, if not all, of your overclocking questions in the Overclocking FAQ written by Bill Hillman.  If that doesn't help try the various overclocking news groups on UseNet or e-mail me and I'll see if I can help.  You can also post your question in the RipNet UK forums and pick the brains of all the people who visit this site.  If you send me a question please give me plenty of details to work with - particularly CPU and motherboard information; this will make it easier for me to find an answer for you - and bear in mind that I'm not an expert either!  There's also a very good tips and tricks section on Ars.Technica  Happy chip frying!

CPU cooling

Your CPU will get hot at the best of times - increasing the speed it's running at by up to 50% can only make this worse.  Heat can be a major problem, since it will lead to instability, crashes, and maybe data loss.  If you're unlucky you may even do permanent damage to your processor, and that will be expensive!

Because of this your CPU will be fitted with a metal heatsink and a cooling fan.  The heatsink sits flush against the chip and absorbs some of it's heat, which is dissipated by the fan.  This excess heat goes into your case however, and hence raises the overall system temperature - your PC should, as standard, be fitted with at least one case cooling fan.  This exhausts the hot air out of the back of the case.  You can find out more about keeping your entire system cool in the next section.

So when you've overclocked your CPU you are going to see a rise in temperature.  You can combat this by replacing the stock cooler with a more efficient heatsink and fan combination.  These are relatively cheap (particularly if you consider how much a replacement CPU is going to cost) and quite simple to fit.  Some of the best known are produced by Alpha, GlobalWin, and ThermalTake.  I use a pair of ThermalTake Golden Orbs - apart from looking very cool (ha ha ha) they also do a very good job.  

If you want to fit Golden Orbs to the chips in your BP6 board please note that you'll have to modify them before they'll fit.  The standard Orbs foul some of the capacitors on the board, so you need to either file them down or do what I did - take a hacksaw to them!  There is a very good "how to" guide on this at BP6.com  The Orbs also have a spring clip mechanism for attaching them to your CPU; you need to position the heatsink on the chip and then twist it to engage the clips - this needs a reasonable amount of force, so be very careful not to damage the CPU - ouch!

Opinions differ as to what a safe working temperature is for a CPU.  With the Golden Orbs fitted mine run at about 40º C whilst crunching a SETI work unit (i.e. at full load), and about 35º C when idle.  Since I overclocked my Celerons as soon as I got them (that was the whole point of buying them after all!) I haven't got any figures for them with standard heatsinks and fans - sorry.

Serious overclockers go further still with Peltier coolers and water cooled systems.  I'll add more about these trinkets when I have the time (so maybe next year....)

 System cooling

This pic shows you what's going on in my system.  It comes from a nifty little utility called Motherboard Monitor.  MBM will keep a close eye on temperatures and voltages for you, sounding alarms if anything goes outside the parameters you've set.  It can even shut your system down entirely if things look like going horribly wrong!

Motherboard Monitor is free, easy to set up, and doesn't take a huge chunk out of your memory.  I recommend it to you, download it here

Note that these temperatures are whilst running a SETI work unit on each CPU (i.e. both CPUs are at full load).  Shows how well the Golden Orbs and case fans work - the system has one 80mm fan blowing in at the front of the case, two exhausting at the rear (one is the PSU fan), and another two exhausting through holes I cut in the side of the casing, opposite the CPU fans.

BX chipset cooling

I also installed a fan to keep the BX chipset cool (Abit now does this as standard on at least one of their boards, the Socket A KT7).  This is a piece of cake to do, here's how:

1.  Get yourself a 486 cooling fan and some heat transfer paste.

2.  Remove the heatsink from your BX chipset (carefully), and then spread a little heat transfer paste on the rear surface of it.

3.  Replace the heatsink - if heat paste squeezes out from the sides you've used too much, so remove the heatsink again, and clean off the excess paste.  Only a very thin smear is required; too much will actually insulate the chipset and it will run hotter!  (Exactly the same applies when you are putting heat paste on your CPUs).

4.  You should now find that the 486 fan rather neatly covers the surface of the BX heatsink; screw it directly to the heatsink, attach the power lead to a spare connector.

5.  Power up the system, sit back, (preferably with a beer but this bit's optional) and admire the fan merrily spinning away and giving much needed cooling to your BX chipset!

MBM version 5.0 is now available.  Works much the same as the previous version but has an updated interface.  Still a little fiddly to set up in the first instance, but once you've spent a few minutes on it you never need to touch it again - MBM just happily runs and keeps a watchful eye on everything for you.  Lovely.

In the not too distant future I hope to add a little article here on how to modify your PC case and add extra cooling to your system.  Watch this space.

Bench marking

Okay so you've successfully got your system flying along at Mach speed.  Applications load faster, gameplay is smoother, and life is sweet.  Is there an objective way to measure the performance you've gained?  Of course - you just need to get yourself a freebie bench marking suite (you may have noticed that I'm a big fan of free software - more details of how to grab some on the Software page)

SiSoft Sandra is just such a utility.  It will check out several aspects of your system and help you to judge whether the changes you're making are having the desired effect.  In addition it'll give you an idea of how your PC measures up against some other fairly common systems (and also a Xeon - sorry did I say common?)

Here you can see what Sandra makes of my humble Celeron 466s.  Nice aren't they!!!!

You can download SiSoft Sandra for free here

As well as benchmarking your whole system there are other more specialist programs available, such as 3DMark.  This checks out the 3D performance of your PC and allows you to compare it to similar systems.  It will also help you to pinpoint areas you can target to gain better quality 3D.  The screenshot below shows how my system performs.  A problem with Celeron CPUs is that Intel built them without the set of 3D processing instructions that the Pentium has, so their mark is always going to be lower than that of a Pentium (or two) running at the same speeds - my old Pentium II running at 400MHz clocked up a 3D mark of 940, not far short of the two Celerons running at 595MHz.  That said a 3D mark of 1095 is reasonably respectable, I think.

I've now added the GeForce 2 GTS - benchmarks will be posted in the not too distant, honest!

You can download 3DMark2000 here

System specifications

All of the results above are from my current system, which consists of:

   Abit BP6 with 486 fan cooling BX chipset
   2 x Celeron 466s, running at 595MHz with 2.1 volts
   ThermalTake Golden Orb CPU coolers
   128MB PC100 SDRAM
   8.4 GB Samsung HDD
   6.4 GB Quantum Fireball HDD
   Creative 3D Blaster Banshee 16MB PCI
   Creative SoundBlaster Live! Value
   Acer 40x CD-ROM
   Trimaxx 200 CDRW/DVD
   Ambient 56K hardware modem

Stability testing

Your newly overclocked system is running at speeds you'd never have dreamt possible.  All your data, applications, and settings have been transferred, all is sweetness and light with the world.  Until you have a major crash and wipe out your hard drive - there go your business accounts, that last round of Q3 you'd saved, or maybe just all those dodgy pics you'd downloaded.

This is NOT the way to find out that your system is unstable.  Far better to do some intensive testing, before you commit anything to your hard drive that you haven't already got saved on some other media.  

"So how do I do this intensive testing?!?" I hear you cry....

Well there are several ways.  The latest 3D games are pretty CPU hungry and will give your system a good work out, but ideally you want to run your PC under heavy load for a looooong time (we are talking several hours, or preferably days, here).  And no matter how avid a gamer you are you're going to be suffering by the end of that session.

Much better to find an application that puts your CPU through it's paces while you wander off and have a coffee, a sleep, or whatever.  Also much better if this application can actually do something useful as a by-product.  Step forward SETI @ Home.  This will run your CPU at 100% load for as long as you leave your PC powered up, and it has data to crunch.  If your new machine will happily churn SETI work units for a couple of days straight without falling over then you can be fairly sure that it's stable; but remember that VERY few things in life are guaranteed!

Here's what SetiStash (an application for running several SETI work units in succession) looks like:

You can download SetiStash here

My PC is left on 24 hours a day normally, and runs SetiStash on each CPU.  About the only thing that ever makes it crash is the demonic Outlook Express, but that's another story.  If you find your system is unstable there are three main approaches to cure it :

1.  Improved CPU cooling

2.  Increased CPU core voltage.  You can set this in the BIOS but take care not to exceed recommended maximum figures!  If you don't know what these are check out these Intel and AMD info sites.

3.  Least favourite option; back off the FSB and hence the CPU speed, until you get to something your PC can handle - but that's not the aim of overclocking is it!

By the way if you fancy joining a SETI team there's still room for newcomers in Watching the Skies!  Join our happy band here

Overclocking graphics cards

Still being worked on - hope to feature the Hercules prophet GeForce 2 GTS here very soon!  (Already got the card from Overclock.co.uk and it's a beauty - just haven't found the time to write up it's review yet!!!)

FAQ

Feel free to e-mail me any questions you've got, but please check out this overclocking guide first.  It first appeared on alt.comp.hardware.overclocking, and was produced by a group of contributors there in response to a barrage of questions; thanks to Bill Hillman and everyone else who had a hand in it's production - hope you don't mind me reproducing it here!  It's a comprehensive piece of work and should provide all the information you need.  If you decide to e-mail me please include a much info as you can about your CPU, motherboard, and so on.  This will make it easier for me to find an answer to your question.  Alternatively you can post a query in the RipNet UK forum

Overclockers links

As time permits I'll update this section to include links to other overclocking related websites.  The intention is to cover not only information sites but also specialist suppliers of overclocking goodies.  Watch this space!

Pitfalls!

Disclaimer :  Get it right and overclocking will give you a high spec PC at a bargain price.  Get it wrong and it can be a complete nightmare!  All the information given on this site is for you to use or ignore as you see fit, but remember that there is an element of risk to this.  You could end up losing data or even permanently damaging your hardware.  I will not be held responsible for any losses you incur!

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