What is Over clocking ??

Clocking is...?

All Pentium CPUs run with clock doubling. That's the way they are built. The PC works with two frequencies, which the user can adjust. The clock doubling is set on small jumpers on the motherboard. You simply set a clock doubling factor, to make the CPU work – but who says that you must use the factor listed in the manual?

If you are brave, you try to set your CPU to run faster than it is designed to run. Often it works. If you "cheat" the CPU in this manner to work faster, it is called over clocking. Over clocking is kind of a PC tuning, which can be fun to fool with – if you are interested in the technicalities of PC-hardware. Otherwise - skip it!.

If you are lucky, you can make a medium speed CPU run as fast as the top of the line version! Please note, I accept no responsibility for the result of your experiments. I will now try to explain the technologies in the over clocking phenomenon. The interesting part is that, like much of the theory I tried to describe in in the modules 3a, 3 b and 3c, it all comes together here in the clock doubling technology.

The CPU works on two frequencies: An internal and an external.

The external clock frequency (the bus frequency) is the speed between the CPU and RAM. In the Pentium CPUs it is actually the speed between L1 and L2 cache. In the Pentium II it is the speed between L2 cache and RAM.

The internal clock frequency is the speed inside the CPU, that is between L1 cache and the various CPU registers.

For practical reasons you let these two frequencies depend on each other. In practice you choose a given bus frequency (between 60 and 153 MHz) and double it up a number of times (between 3½ and 8). The latter frequency become the CPU internal work frequency.

The CPU frequency is the result of the the bus frequency multiplied with a factor. If you increase the bus frequency, it affects the CPU frequency, which is also increased.

What is Over Clocking...??

Since clock doubling and bus speed can be freely adjusted on the motherboard according to your desires, you can in principle make the CPU run at 600 MHz. You set the bus to 133 MHz and the clock factor to 4½. Then the CPU runs at 600 MHz – if it runs. The question is whether the chip will tolerate that - and if it will give a stable performance, since clock doubling means more than added heat.

We have now seen that there are two frequencies which can be manipulated, if you want to re-clock the CPU:

The bus frequency can be increased, let's say from 133 to 153 MHz.

The CPU frequency can be increased. That can happen as a result of an increased bus speed, which also affects the CPU frequency, or it can happen by using a greater clock factor. The latest is not possible anymore.

Both techniques result in a faster PC. If the bus frequency is increased, it affects all data transport to and from RAM. It will work faster, to the joy of all work done on the PC. However, the RAM has to cope with the increased speed.

When the CPU internal frequency is increased, many applications will be happily affected.