PROCESSOR
OVERCLOCKING
Get maximum output from your
processor
A few months ago, I had no idea how to begin the process
of overclocking my machine. It was painful even trying to figure out what
questions to ask. This write-up is aimed at those just starting the process. It
tries to provide you with the particular steps needed to undertake, investigate
further, and produce some level of overclocking.
You should understand that there are various degrees of
overclocking, however, the initial steps associated with running a faster
Front-Side Bus (FSB) that will produce the greatest gains. You can continue to
tweak almost forever for small gains that are of little value in terms of
observable performance, and you may undertake those just because it is fun for
you. Nothing wrong with either perspective.
To understand overclocking, you need to realize that for
the majority of mobos (motherboards), there is a single clock which controls all
operations made by the computer. The various operations (for example graphics)
are slaved to the clock.
The clock measures time in what is typically called a
tick, cycle, period or the clock refresh rate, and reflects a discrete measure
(small-fixed unit) of time. The cycle is also commonly converted to an
operational frequency, (frequency = 1.0 / period) in many discussions. For
example, a clock cycle of 7.5 nanoseconds converts to a 133 MHz clock speed.
(The clock cycle can be viewed as a square wave for those familiar with such
representations. The cycle is thus made of a positive half and a negative half.)
Because the various computer operations are often slaved
to the single clock, a balance of the various device speeds must be achieved so
that each device is stable.
The clock controls the Front-Side Bus (FSB) and the
different components use that bus speed to determine their own speed. With a
single speed available from the FSB, this creates the need for multipliers, a
term you often hear.
Some multipliers increase the FSB reference speed for use
by their component, for example the CPU multiplier is typically greater than
one; for example, an AMD XP 2100+ is set at 13 when the CPU is locked. Others
slow it down; the PCI bus, for example, typically uses a multiplier of on many
of today’s motherboards.
If the multiplier slows the speed down, it may also be
called a divider. For this discussion multipliers and dividers are viewed as
performing the same operation, i.e. changing the FSB clock speed for use by
their particular devices.
One definition of overclocking is the process of
balancing the various component speed needs to produce stable operation at
different FSB speeds.
When you have the freedom to select the multipliers for the various devices (hard drive, video, memory, etc.), this balance is easier to obtain. That statement may not be obvious to you now but hopefully will be better understood later as we deal with the combination of memory and CPU. Ultimately, what we would really like to do is work with each device independently. Motherboards are available that allow this separation are becoming more widely available.
Processor Overclocking
FAQ
What is the purpose of this FAQ?
I
don't intend for this FAQ to be THE definitive overclocking FAQ, but I'd like it
to give a general understanding of overclocking.
What is overclocking?
Overclocking
is the practice of running your processor / system bus / graphics card or other
peripheral at a faster speed than it is intended to run at.
Can it damage my equipment?
Yes, so
don't do it unless you are willing to assume the risk. Anyone that talks about
overclocking isn't going to buy you new equipment if you damage it by doing
something crazy like running it over specified speedsJ
!
Great! How can I do it?
Well, I'm
only going to focus on the processor / system bus overclocking. If you want to
overclock your graphics card, you'll have to look elsewhere for details.
Is Proper Cooling
necessary?
If you want to overclock your processor, you've got to figure out some things first. To prepare, you must have a good heatsink with a fan blowing on it. The heatsink should be held in place with a bracket and there should be thermal gel in between the heatsink and processor. Heat is the main cause of overclocking failure, so make sure you keep it cool.
What about System Bus speed and
multiplier?
Your processor runs at a speed
that is derived from two variables: system bus speed, and the clock multiplier.
These variables are set on the motherboard, either by jumpers or by your
computer's BIOS. Either way, you have control over them. For example, if you
have a Pentium II 450 processor, and you know the bus speed is 100MHz, you set
the motherboard to 100MHz, and the multiplier to 4.5 (4.5 * 100MHz = 450MHz).
That's it! If you want to overclock the chip, you either up the bus speed, up
the multiplier or both. You can also separately up the bus speed and reduce the
multiplier or vice versa. Your only limitations are the bus speeds and
multipliers that your motherboard can support. Thus, if you bought the fastest
chip your motherboard supports, you may not be able to overclock.
Some processors will not allow you to change the multiplier. Most, however, will allow you to change the motherboard multiplier and bus speed without incident.
Bus Speed and the ISA / PCI
bus.
When you increase the bus speed from say, 66MHz to 75MHz or from 100MHz to 112MHz, 125MHz in addition to upping the processor speed, you are also upping the speed at which the processor is talking to memory and usually the speed that your PCI cards are running. At 66MHz, the PCI bus speed is cut in half, so the PCI bus runs at 33MHz as it is supposed to. At 100MHz, the PCI bus speed is cut into a third, so that it still runs at 33MHz. However, at the in-between speeds such as 75MHz, 83MHz, or 112MHz, the PCI bus speed still goes with the half or third multiplier and the PCI bus is overclocked. Running your PCI bus at 37.5MHz or 41.5MHz can cause some whacky problems, so you must be careful of that. Also, if you have any ISA cards, bumping up your bus speed may cause the ISA bus to run faster. Pull you ISA cards out temporarily if you think they may not be able to handle a little more clock.
Bus Speed and Memory.
The bus speed
of your system, in addition to controlling the speed of the PCI and ISA buses,
also directly affects how fast the processor communicates with memory. Standard
SDRAM is spec'd to run at 66MHz, but can often run faster. If you get 100MHz
SDRAM, you should be able to up the memory bus to 100MHz with no memory
problems. As bus speeds increase, memory specs will also increase. I recommend
buying the highest spec'd memory you can, considering bus speeds that you will
be running at.
Voltage at higher clock
speeds.
Processors all run at fairly specific voltages that are the
lowest they can be to still run the processor and to keep the heat down.
However, if you are running your processor at much higher speeds, you will need
to up the voltage. If you bump up the speed, and the processor is still cool,
but you can't boot properly, try more voltage.
Motherboard manual.
I can't stress
this enough, but you've got to have your motherboard's manual. If you don't know
which jumpers to change, or how to get into your BIOS and manipulate the
settings, you can't overclock anything.
I'm Ready! How do I start?
Start in
small increments. Bump up the bus or multiplier, and see if your system still
boots. If it boots, run some processor intensive application such as Quake and
play it for an hour or two. If it's still fine, you may want to go higher. The
higher you go, the greater the risk of failure. You definitely want to start on
a very stable system. Don't overclock a system that crashes every hour. When you
hit the upper peak, and your system won't boot, see how hot the heatsink feels.
If it feels really hot, then you may need more cooling to run at that speed. If
it is cool, and your PCI bus got bumped up, then you may have a card that
doesn't like to run faster than 33MHz. You could replace it - or take it out of
your system. Alternately, you may have memory that doesn't want to run at the
bus speed you set. Replace it with higher tolerance memory that is spec'd to run
at the bus speed you set. If the heatsink is cool, and you didn't do anything to
the bus speed, you may need to up the voltage to the processor. Doing this is
guaranteed to make the processor run hotter, which may or may not be a big deal.
That's it in a nutshell.