Note : Most of the chips featured in this article are discontinued - it may be possible to find them in some parts of the world or on the second hand market. The details here are however a useful primer for overclocking in general. The underlying principles are still the same, but you can't guarantee that the latest processors will overclock so well. Good Luck.

Before I begin, it’s important to stress that anything you attempt after reading this article is entirely at your own risk. These chips were not intended for this use and following these procedures will invalidate your warranty. Please do not try and hold me responsible for anything that goes wrong. Right, that’s my arse covered, if you’re still with me then read on – it could save you some serious cash. To give you an idea of what you could be missing, take a look at my benchmarks page and see what you can achieve.

Table Of Contents

Introduction
What Is A Celeron ?
What Is Overclocking ?
What Do You Need To Overclock?
        MotherBoard
        Memory
        Case
        CPU
        Other Parts
Assembling The Components
Overclocking Your Chip
Tweaking Your System
Stress Testing
Utilities
Links
Tips & Tricks
       

Introduction

Since I started writing my PC benchmarks page I’ve been inundated with requests for more information. Well, I had to start somewhere too. Finding the information required can be a bit of a minefield. In the last six months I’ve hung about in several hardware Usenet newsgroups and message forums. I’ve gathered as much information as you will need to either upgrade your current PC, build something new from scratch, or create a complete hybrid. This item is aimed mainly at the upgrader. How annoying is it to have bought a machine 2 years ago, only to find it’s out of date?

Personally, I’m a gamer, a hobby which requires a real powerhouse to get the most out of it. I’ve built, or helped build several overclocked Celeron machines in the last few months just to increase my (and my friend’s) gaming pleasure.

So what is a Celeron?

The brains behind it all, and the component that’s going to take the stress of overclocking. Before I go on to suggest what chips you should look at, it’s important to understand how multipliers and bus speeds combine to give the overall processor speed.

Celeron processors were designed to be used on motherboards with 66Mhz bus speeds (it’s actually 66.6). The multiplier is the factor that 66 should be multiplied by to achieve the speed that Intel designates the chip. For example a 266 chip has a multiplier of 4 (66.6 x 4 = 266), while a 300 chip has a multiplier of 4.5 (66.6 x 4.5 = 300). On all new Intel chips this multiplier is locked and cannot be changed. Therefore to overclock we need to change the bus speed.

As these Celeron chips are fabricated to the same standard as modern 100Mhz Pentium II, most of them also run at 100Mhz as well as 66. Therefore what was a 266 with a multiplier of 4 can run at 400. A 300 with a multiplier of 4.5 can run at 450.

There are 3 chips which are I’d recommend trying. I’ve had success with the first two, but not yet had a chance to try the SL2W8 option.

1. Celeron 266 (0k cache). The retail version of this chip, which includes a heatsink and fan, are great overclockers. Mine runs flawlessly at 448Mhz (Multiplier of 4 with a bus speed of 112Mhz). As this chip has no second-level cache it’s performance is somewhat hampered when using Windows applications. However, if its games you’re interested in, then this is an excellent choice and a bargain at the price.
2. Celeron 300A (128k cache). About 80% of these chips are reckoned to overclock to 450Mhz (4.5 x 100) and higher. Out of the 300As I’ve seen, 3 out of 4 have worked at this speed. These were all OEM versions rather than retail. It’s possible that better results can be achieved with the retail version (which also includes a heatsink). Due to the cache configuration on this CPU (it runs at full speed rather than half speed as on a P2) it will in many cases outperform a real P2 450 when overclocked. My current system is based on this chip. It required a little tweaking to get it stable, other than that it’s been flawless and extremely quick.
3. Pentium II 300 SL2W8. Not a Celeron at all but worth a mention. The SL2W8 is marketed by Intel as a P2 300, however most are re-badged P2 450s. Unfortunately buying one is not so easy. There are several different SL2W8s with varying cache speeds, their ‘overclockability’ will vary from chip to chip. These are probably best left alone unless you can find a dealer that will assure you are getting the right one. In the UK this is quite a hard proposition.

• Other Components

Any other components are not critical to overclocking a system. Providing you stick with the 100Mhz-bus speed only the CPU is overclocked. I mentioned earlier that I had the bus speed set to 112Mhz for the Celeron 266. This does put extra strain on hard drives and PCI cards so I’m not going to recommend it in this guide. It’s only worth experimenting with this once you’ve convinced yourself you have a stable system running at 100Mhz.

Assembling the parts.

Ok so now you know what parts you need. Now it’s just a matter of putting them together. I’ve done this many times before and find it second nature now. If it’s the first time you’ve looked at PC components it can be quite daunting. Don’t worry it’s very hard to do any damage. Take notice of all anti-static warnings and purchase a wrist strap if you are really paranoid.

Next is to get the motherboard ready for the CPU. Abit motherboards come with a retention bracket that is designed for a Pentium II chip. It’s not ideal for use with a Celeron but it’s good enough. If you’ve bought a different brand of BX board then refer to the instructions supplied. I’ll go on to describe how the Abit stuff fits together.

There are two small semicircular brackets that fit under the motherboard and poke through to the top either side of the CPU slot. The retention bracket sits on top of these, once on they can be tightened with a screwdriver. If you want to check that the CPU fits in OK then try it out now. Don’t push it in all the way, just make sure you’ve got everything around the right way.

Now screw the motherboard into the case. It should be fairly self-explanatory which way around it fits in. Make sure the slots on the motherboard line up correctly with the slots at the rear of the case. The screw holes in the motherboard will line up with those on the case. Put each screw in and tighten lightly. Once they are all in tighten them up. There are several connections that need to be made between the case and the board. Primarily there is a large rectangular connector, which is for power. This only fits around one way, make sure it’s in firmly. Then there’s a whole tangle of cables leading from the front of the case, these control things like the power switch and hard drive lights. Check in the motherboard manual for exactly where they go.

Now the motherboard is in, you can start adding the rest of the components. There’s no definitive order on doing this but try and work out where everything is going to fit beforehand. This way you can avoid taking items in and out which get in the way of each other.

It’s probably a good idea to get the CPU in first. The heatsink’s fan gets its power from a small 3-pin connector on the motherboard – these can be hard to get to when your other peripherals get in the way. Push the CPU into the slot – make sure it goes all the way in, it’s quite easy to leave it half way out. If you do this, the machine won’t even power up (but you probably won’t do any harm). Once in, connect the small lead from the heatsink onto the 3 pin connector I mentioned before.

Next put in the memory. Check the motherboard manual for RAM slot 1. Then look at the raised lips along the slot. Compare this to the DIMM chip and you’ll realise it can only fit in one way. Push it in. As you do the two retention clips will close around the chip. Job done.

These are all the new components together. Now it should be just a case of moving the remainder of the parts from your old machine into the new. Most of it should go in similar locations to where it was before. Refer to the motherboard manual for the correct orientation on connectors – remember that the red stripe on ribbon cables goes into pin position one.

If you’ve upgraded from an AT case and motherboard you should be impressed with how tidy everything now looks.

It is a good idea at this point to get your system up and running before proceeding to the overclocking step. Test out your applications to be sure everything is working correctly and that you can access all your drives. If you attempt to overclock straight away and encounter a problem, you won't be sure if it's the overclocking that's caused it, or it was a problem before.

The overclocking

Now for the serious part. This is where we can get the big performance boost, just with the press of a few buttons. Everything that follows is particular to Abit motherboards. On other boards you will have to tape over pins on the CPU and set jumpers to get the same results with Abit you can do it all in a menu.

It’s time to get familiar with the Abit Softmenu. Power on and you should see the initial BIOS (Basic Input Output System) start up screen. Hit the <Delete> key during or shortly after the memory test and you should be presented with the following CMOS setup: (you've probably already been here to detect your hard drive)

Select the CPU soft menu option and you should end up here:

If this is the first time you've been into this screen then it will look a little different. The CPU Operating Speed will report what it thinks the chip should be running at. A Celeron 266 will show 266(66) while a 300 will show 300(66). Select this option and use the <Page Up> and <Page Down> keys until User Define is highlighted. Once this is selected then all the above options will become available.

Move the cursor down to the External Clock option and change it until it reads 100Mhz. Now change the Multiplier Factor until it is the same as your chip - a 266 should be set to 4.0 while a 300 should be set at 4.5. As this is the first time you've attempted to overclock, don't change anything else now. Escape out to the main CMOS menu and select Save & Exit Setup. Reply (y)es and your system will reboot.

All being well the intial boot screen will appear and report you now have a Celeron MMX at 450Mhz. If you've got a really good chip then it will boot all the way into your Operating System (OS) with the default settings. This doesn't necessarily mean the system will be stable - you will have to stress test it to make sure.

If you booted but got a message saying that the 'CPU is Unusable or Has Changed' then re-enter CMOS and change Speed Error Hold to Disabled.

If you didn't get as far as the Operating System or you were left with just a blank screen then there's more tweaking required. Reboot.Get yourself back into CMOS setup by holding down <Delete>. If you were left with a blank screen then you will probably have to power down and reset the CMOS to defaults. To do this, power up whilst holding down the <Insert> key. You should be back in the CMOS setup screen again. Time to do some more tweaks.

Tweaking to get a more stable system

If you found that you couldn't boot, or you were having errors in your OS then there's some more playing that we can do to get it to work. Warning! What follows could fry your CPU. I've had to follow this procedure several times before and not had a problem - remember this is at your own risk.

To get the CPU stable we need to give it some more power. You should be back in the CMOS Soft menu: