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Warning : if you overclock your processor or graphics card you will invalidate any warranty

Just after I'd bought the Celeron 533 above, the Celeron II 566 FC-PGA (Flip-Chip Pin Grid Array) appeared two months later, still based upon the 66MHz FSB (Front Side Bus - or main system bus speed). Looking around various web-sites, it was apparently easy to overclock these to 850MHz by using a 100MHz FSB.

The new Celeron II's were known as "coppermines" and the reason they have good overclocking potential is two-fold:

  1. They were based upon the same process as their big brothers, the Pentium III coppermines which run at 100MHz FSB - so why shouldn't the Celeron II's?
  2. They run at 1.5V default as opposed to the Pentium III which is 2.0V.

Basically, in simple terms, the Celeron II's were the Pentium III's with half the cache and a poorer quality yield and a damn sight cheaper as well.

Armed with the knowledge gained from the web I decided to take a gamble and have a go - I couldn't resist it! Therefore the following components were changed in my system:

Pictures of some of these components and the other components of that system are shown below. Click on the thumbnail to see a larger version:

Abit BX6 Rev2 Celeron II 566 FC-PGA GlobalWin FKP32
Abit BX6 Rev2 Celeron II 566 FC-PGA GlobalWin FKP32
Voodoo5 5500 VideoLogic SonicVortex2 Vasco T-217 ATX Case
Voodoo5 5500 VideoLogic SonicVortex2 Vasco T-217 ATX Case

Once the system was installed and up and running it was time to see what it was capable of. Before you look into overclocking you have to note a number of factors to watch out for:

  1. Clock multiplier
  2. FSB changing
  3. Voltage
  4. Cooling

From that list, all but cooling could be handled via the BX6 Rev2 "SoftMenu II" BIOS. This was one of the main considerations when choosing the motherboard originally as I had always intended to do some overclocking at some point. Abit are renowned for the overclocking potential of their motherboards - rarely using jumpers and mainly allowing adjustments via the BIOS. Most other manufacturers choose to either use jumpers or no overclocking features what so ever.

Let's look at each of these aspects of overclocking in turn - with particular reference to the system I chose.

1. Clock multiplier

With the first Pentium II's and Celerons, these processors were not clock-locked and overclocking could simply be achieved by adjusting the clock multiplier via jumpers on the motherboard. For example, a Celeron 300A had an FSB of 66MHz and a multiplier ratio of 4.5. Therefore 4.5*66 = 300MHz (rounded up). All you had to do was adjust the multiplier to a bigger ratio and hey presto - a faster processor for your money.

Unfortunately, both Intel and AMD (the biggest processor suppliers) decided for their later products to lock the multiplier - removing this option. For the Intel Celeron and Pentium series there's nothing you can do but for AMD's Athlon and Duron processor's there's a loop-hole. More on this later when I come to my Duron system :).

2. FSB changing

Another option is to adjust the FSB or main system clock speed. There are 3 main FSB's supported by processors at the time of writing - 66MHz, 100MHz and 133MHz. This is not locked by the processor and can be set by the motherboard. Whether the processor will run at these speeds depends upon the type and also the quality of the die and architecture.

Celeron Based upon the Pentium II architecture and process so may run at 100MHz
Celeron II Based upon the Pentium III architecture and process so may run at 100MHz
Celeron II (800MHz+) Latest processors still based upon Pentium III which now supports 133MHz so they may run at 133MHz
Duron Based upon the Athlon "Thunderbird" architecture which will soon support a 133MHz bus so these may run at 133MHz

The FSB also has a direct relationship to the other busses on the system.

The table below shows which processors support which bus speeds and the ratios for these busses:

Bus speed Intel AMD AGP PCI ISA
66MHz Celeron I/II N/A 1/1 2/3 1/4 PCI
100MHz Celeron II 800
Pentium II/III
2/3 1/3 1/4 PCI
133MHz Pentium III Athlon 1/2 1/4 1/4 PCI

Due to the table above you have to beware when using non-standard FSB's. An AGP, PCI or ISA card my not work or may not be stable. ISA devices are notorious for causing problems and can become damaged beyond repair in some circumstances. Therefore my advice would be to stick to the standard FSB's.

Note also that memory is available at speeds of 66MHz, 100MHz, 133MHz and now 150MHz. Running PC100 memory at 133MHz may work - then again it may not.

System specific

The Abit BX6 Rev2 in the system I built had the following bus speeds available FSB (PCI): 66MHz (1/2), 75MHz* (1/2), 83MHz* (1/2), 100MHz (1/3), 112MHz* (1/3), 117MHz* (1/3), 117MHz* (1/4), 124MHz* (1/4), 129MHz* (1/4), 133MHz* (1/4), 138MHz* (1/4), 143MHz* (1/4), 148MHz* (1/4), 153MHz* (1/4). Those highlighted with a * indicate the non-standard values which may have caused problems with that system.

3. Voltage

If you do decide to try and overclock a processor you're probably going to need to increase the core voltage to achieve a higher speed.

The specifications for the most common processors already covered are available from these sites (it's best to right-click and choose "Save as" and you'll need Adobe Reader from here):

Manufacturer Processor
Intel Celeron (all models)
Pentium II (66MHz)
Pentium II (100MHz)
Pentium III (Slot 1)
Pentium III (Socket 370)
AMD Duron (Socket A)
Athlon (Slot A)
Athlon (Socket A)

To find out which processor you've got grab a copy of CPU-Z.

System specific

In the case of the Celeron II 566MHz the nominal Vcore is 1.5V with a maximum of 2.1V. Note that Intel state "Functional operation at the absolute maximum and minimum is not implied or guaranteed. The processor should not receive a clock while subjected to these conditions"

As the Celeron II based upon the Pentium III (Socket 370) who's nominal voltage is 1.65V it should be safe to at least raise the voltage to this level.

The Abit BX6 Rev2 in the system I built had the supported voltages from 1.5V through to 3.5V.

4. Cooling

When you raise the voltage or clock a processor at a higher speed than specified the temperature will increase as a result because it's being stressed more. Therefore you have to look at better cooling to get the temperature down.

The heatsink and fan supplied with retail boxed processors in most cases will not be up to the job. Therefore you have to consider a better solution. Additional case cooling with an inlet fan at the front of the case and an exhaust fan at the back of the case (behind the processor) will also help.

System specific

For the Celeron II 566MHz I chose the GlobalWin FKP32 pictured above which is specially designed for this processor package. With the clamp secure the heatsink sits at the right height above the processor body on top of the "slug" which is the raised part of the processor.

When installing the heatsink and fan it's important to make sure there's a good contact between it and the processor and for it to be level. You should also use a thin layer of a good heatsink compound or thermal grease in between the heatsink and processor. Most web-sites recommend "Arctic Silver" which is pictured below. In my case I used standard thermal grease.



By changing the FSB on the Abit BX6 Rev 2 to 100MHz and setting the Vcore voltage to 1.6V I was able to get the Celeron II 566MHz running stable at 850MHz. The temperature under full load (measured via the CPU's internal thermal diode) was 50C compared with the maximum of 90C.

So, if you're willing to have a go and stay within reasonable limits you can gain up to a 33% increase in processor and therefore system speed.

If you want to advertise on this page please E-mail me at paul_at_paulslounge_dot_co_dot_uk

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