How do I overclock my computer ?
- Changing the bus Speed
To understand how you can overclock a Pentium, Pentium Pro, 6x86, or K5 CPU, it helps to
realize that the internal clock in these CPUs runs at a different speed than the external
clock or bus speed. The external clock is the speed at which the cache and the main memory
run and when divided by two yields the speed of the PCI bus. There are only three
different official bus speeds used by the Intel Pentium, Pentium Pro, and the AMD K5 CPUs
- 50, 60 and 66 Mhz. The 6x86 uses five bus speeds: 50 MHz, 55 MHz, 60 MHz, 66 MHz, and 75
MHz. There are also new boards available which support the unofficial bus speed of 83 MHz.
Always go slowly and increase the bus speed one step at a time (e.g. go from 60 Mhz to 66,
not 60 Mhz to 75). This is the most successful way to overclock. Using this method, almost
every P150 CPU runs at 166 MHz and most all 6x86 P150+ CPUs run at a P166+ level or 133
Mhz.
- Changing the Multiplier
The internal clock is controlled by an internal clock multiplier in each CPU which is
programmed via CPU pins. Intel Pentium CPUs support the following multipliers: x1.5, x2,
x2.5 and x3. Intel Pentium Pro CPUs support x2.5, x3, x3.5, x4. 6x86 CPUs so far only
support x2 and x3, but the upcoming M2 will support x2, x2.5, x3, x3.5. The K5 is kind of
a difficult fellow here, because it doesn't seem to be affected by the external settings
of its multiplier. So far it only uses the x1.5 multiplier for each of the PR75, PR90,
PR100, PR120, PR133 CPUs. The new PR150 and PR166 K5 CPUs will use the x2 multiplier, but
it seems fairly likely that you won't be able to change it - although I have not been able
to verify this.
To change this setting, find something like 'CPU to BUS Frequency Ratio Selection' in your
motherboard manual. There are usually two jumpers used to change these settings.
- Changing the CPU Supply Voltage
Often the change from STD to VRE voltage is the whole trick to successful overclocking.
This is due simply to a bigger voltage difference between the digital high and low
conditions, which results in better signals for the CPU and other motherboard devices. If
you can't run your CPU reliably at one particular clock speed, it's always worth
considering changing to a higher supply voltage. The silicon of STD and VRE CPUs is
identical, so you won't damage your STD voltage CPU with VRE voltage, the CPU will only
run a little hotter.
Get me back to the overclocking section
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