OverclockingOverclocking
Overclocking
28 MA XIMUMPC MARCH 2006 MARCH 2006 MA XIMUMPC 29
Overclocking 101
Understand the basics before you embark on any overclocking project
HOW DOES YOUR COMPUTER
DETERMINE YOUR CPU’S SPEED?
If you’ve ever wondered just how your system tells your
CPU what speed it should run at, the answer is easy.
The default clock speed is stored on your CPU, and it’s
calculated using simple math. If you can multiply two
numbers, you can calculate your clock speed.
The fi rst number is your system’s front-side bus
(FSB) speed. On most systems, the front-side bus is the
main conduit for information between the CPU and the
rest of the system. Its speed is measured in megahertz
(MHz). The second number is the CPU multiplier, which
is an internal setting that is established by the manu-
facturer. To calculate the CPU clock speed all you do is
multiply the FSB speed by the CPU multiplier.
So, if we have a FSB speed of 200MHz, and a CPU
with a multiplier of 10, we multiply 200 by 10, and you
can see we have a 2000MHz, or 2GHz, CPU.
WHAT IS MULTIPLIER LOCKING? HOW
DOES IT AFFECT OVERCLOCKERS?
CPU manufacturers prevent most CPUs from operating if
you change the CPU multiplier in the BIOS. This isn’t really
an anti-overclocking measure, it prevents unsavory vendors
from taking slow, cheap CPUs and selling them as more
expensive, higher-clocked CPUs for huge profi ts. The über-
high-end CPUs, like the Athlon FX and Pentium Extreme
Edition chips are not multiplier locked.CAN YOU OVERCLOCK ALL CPUS?
The short answer is no. Some CPUs overclock like
there’s no tomorrow, while others might only go a
smidge higher than stock. Here’s why: To make a
batch of CPUs, a huge silicon wafer is created that
contains dozens of identical CPU cores (see left).
The little cores are then cut from the wafer and
tested for speed and stability. Because of manufac-
turing variances, only a small portion of the chips
will run at the highest speed possible at a reason-
able temperature, and the rest will be set to run at
lower speeds. Sometimes, when the demand for
the slower chips outstrips the demand for über-fast
chips, chip vendors will sell chips that could run
at a higher clock speed at a slower speed. These
chips are the absolute best for overclocking, and
should be sought out!CAN I OVERCLOCK MY DELL,
HP, GATEWAY, ETC?
Probably not. Most OEM system builders make over-
clocking impossible by limiting user adjustments to key
overclocking settings such as front-side bus speed, the
CPU multiplier, and the core voltage.WHAT IS CORE VOLTAGE AND WHY IS IT
IMPORTANT TO OVERCLOCKING?
CPUs are designed to operate at one certain voltage; however,
bold overclockers can squeeze out a few more MHz of perfor-
mance by increasing the voltage running through the CPU. It’s
similar to punching the throttle on a car; you can’t go faster
unless you use more gas.
To give a real-world example, the 3.46GHz Pentium Extreme
Edition processor we overclock later in this story has a core volt-
age of 1.3 volts. To get the chip to run at 4.44GHz, we had to
increase the core voltage to 1.45 volts. Cranking up the voltage
is the most dangerous part of overclocking, and greatly increases
the chances of frying something. As a rule of thumb, increasing
VCORE beyond 10 percent of the default voltage is risky.