Im going to start this guide with the latest and greatest trend setting cpu's, the duron and t-bird cpu's from AMD. With so many systems and cpu's out there it can get a little confusing. So im going to try and un-confuse you. Now the stock AMD cpu's are all multiplier locked, at one time the durons were not, if you look at the pic , you will see what a unlocked Duron L1 bridge looks like.
The pic is of a Factory unlocked Duron 800, you can see that the L1 bridges are connected. Dont ask for one of these as only a few tech sites are supplied with unlocked Durons etc. The next picture will be of a stock Factory for retail Duron 800 .
Note the gaps in the L1 bridges, all you need to connect the bridges is a led pencil, this will unlock your cpu multiplier, allowing you to change the multiplier in the bios, or through the manual jumpers .
On to OCing your cpu.
Now you have a Duron / T-bird cpu that is unlocked, to over clock the cpu you only have to increase the multiplier. EG: 8x multiplier by 100mhz bus speed = 800mhz cpu clock. To over clock , try 8.5x multiplier by 100mhz bus for 850mhz cpu clock. You increase the multiplier until the puter no longer runs stable or refuses to boot. Which ever comes first. At this point let me tell you that good cooling is a must, as well as case ventilation. Once you run into boot problems or stability problems, you can increase the voltage to the cpu, 3 tenths of a volt being the accepted maximum increase. With today's MB's we can increase the voltage one 20th of a volt at a time. Depending on how far you want to go, you may need proactive cooling like a peltier to allow higher cpu clock speeds. How far should the Duron 800 OC ? There is no standard answer for this, as all cpu's are not created equal . But a good 50% or so reach 1ghz 10x 100 = 1000mhz and a even better portion can do 9.5x100= 950mhz. Depending on the MB , you can also try 133mhz bus speed EG: 7x133=931mhz 7.5x133=997.5mhz etc. 133mhz being a standard bus speed means that you computer will not be running out of time, but will be running faster than at 100mhz bus. To get the max out of your CPU you can also try different bus speeds, 105mhz 110mhz etc, remember though that your system will be out of time at these non official bus speeds, and as a result may be less stable. Keep in mind that a system thats really OCed to the max but crashes all the time , is no where near as fun as a system OCed reasonably, and runs stable.
Other Unlocked CPU's
The original pentium cpu's are unlocked , Pent 1 MMX 133,166, 200, 233. As well as all AMD K6-2 and K6-3 cpu's. So you can overclock them the same way as a unlocked Duron cpu.
All pent 2 and P3 P4, as well as celeron cpu's are multiplier locked. There was a Japanese web site that used to show how to unlock a celeron 466, but I dont know what came of it. To say the least it was not a bush league operation. So for now we are going to treat the cpu's as locked for good. This means that the only thing we can do to effect an overclock is to increase the bus speed. Taking my old 566FC-pga coppermine as an example. Stock settings were 8.5 x 66mhz bus = 566mhz cpu clock at 1.5Volts . With good cooling ( global win fop32 ) the cpu would OC all the way to 100mhz bus speed for a cpu clock of 850mhz. Most 566FC-pga coppermines would do a 50% OC if not more if it were a particularly good cpu. My 800mhz FC-pga celeron is built on the 533core , and will OC to 1ghz , this is a 25% oc and is more or less the norm. Maybe 25% of the 800 celerons may do 133mhz bus for 1064mhz or a 31% OC.
The same goes for the P3 and P4 cpu's, the only way to effect the overclock is through bus speed increases, and as before , when the system becomes unstable , or refuses to boot , increase the voltage.
Increasing the voltage to the cpu allows for increased overclocking and stability. This also increases the temperature at which your cpu runs at, and without really good cooling , damage may result . In recent years there has been a fair bit of development put into creating coolers capable of cooling overclocked cpu's. With the ever increasing speed of cpu's , means that the heat put out by these cpu's is also on the increase. To fight the heat , ever finer cores are in development , that run on lower voltages, which means that the core itself is becoming more fragile to voltage increases. Keep this in mind. The old celeron 466 would tolerate a half volt increase, but doing this to a 18micron core celeron FC-pga could very well fry it. My 566 celeron would only take 2 tenths , any more and it would not boot. My 800 celeron takes the full 3 tenths and runs fine. Currently my 800 is doing 992mhz with a 2 tenths increase in voltage. Im hoping that after some running at this speed it will do 1008mhz at the same voltage. Remember , good cooling is a must if you are to get the most from the cpu, my cooling set up is a Global Win WBK32 externally ducted. ( see externally ducted fop32 story in reviews )
Stock bus speeds on all MB's are 66mhz 100mhz and recently 133mhz.
This means that at these bus speeds all peripheral ( graphics card , HDD's
, sound ) and what ever else you have plugged into your system run at the
correct speeds. Stray to far and your system will go out of time and
suffer from stability problems. It all depends on your system , some HDD's
dont like being out of spec very much at all, the same goes for sound and
graphics cards. So the closer to standard bus speeds that you can maintain
while ocing the better. My system has a tolerance of about 3mhz PCI speed
+ or - from stock before showing instability. So remember, just because
your system is unstable , it may not be your cpu , but rather the system
being to far out of time. EG: My celeron 566 would lock up at around 80mhz
to 85mhz bus speed, but would be stable at 90 and 95 mhz bus speeds. If I
remember correctly at 80 mhz bus my PCI clock was 40mhz and at 85mhz bus
the PCI was 28mhz. So my stable bus speeds for OCing the 566 were limited
to 70mhz bus , 75mhz , 90mhz , 95mhz and the default 100mhz bus, with the
default PCI clock being 33mhz.