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A BEGINNERS GUIDE TO OVERCLOCKING

Get more from your processor and memory!

Overclocking can be a great way to get better performance from your computer without having to spend any additional money.

By definition, overclocking means pushing your computers processor, memory or graphics past their rated limits in order to make them operate faster and thus give the impression of a better performing system.

The problem is that overclocking can potentially cause damage to your computer if not done properly.  There are a number of different things to consider that will help you gain the best performance, while reducing the risk to your computers components.

Your Computer.

For the Purposes of this article you can assume that your computer consists of a CPU (processor) connected to some memory (RAM) by a motherboard, all the resources needed by the CPU are contained within this memory (including instructions and data).

Overclocking is the process of ‘speeding up’ any kind of hardware with a clock (a precisely timed oscillating frequency). Every clock cycle your hardware performs an operation, this means that you can increase the clock frequency to a point where the instruction that takes longest to perform only just fits within this cycle.

Most manufacturers will void your warranty when you overclock, but if you are careful there is very little risk to your hardware. Please read the whole of this article before trying anything.  We can not be held responsible if you damage your system!

This article is a beginners guide, so make sure to get as much information as you can from other sources before proceeding.

The Silicon Lottery.

No processor can be made perfectly with current technology, each one produced will have different defects, causing instability above a certain clock frequency, at a certain voltage.

What this means is that every processor will only operate at a certain speed before you experience problems.  This speed will always be quicker than the one on the box, but by how much is anyone’s guess.

You may have noticed that there are several processors on the market that differ only by their clock frequency, This is because of a process manufacturers use called binning.  Binning involves testing the chips at several clock frequencies, and putting the chips in ‘bins’ to be sold at the speed of the highest test they pass.

This means that if you’re lucky you can bring your processor’s clock frequency up to just below the speed of the next highest frequency on the market with no voltage increase (we’ll get to that later).

Increasing The Clock.

Most of the overclocking options (if your computer supports them) will be in the BIOS of your computer, the Basic Input Output System.  This is the memory the processor reads when it is switched on.

To change the settings on this chip you need to press a key (usually delete or a function key) during the Power On Self Test [POST].  This will happen every time you turn your computer on or restart it and will usually consist of a splash screen of your BIOS/motherboard manufacturer.

Please note that the BIOS is non-volatile memory, this means it holds its values after the power has been switched off. If you set your values to a very unstable overclock you may well not be able to see the POST when you turn on your computer and therefore not be able to change the values back in this way

Please be familiar with the procedure for clearing your motherboard CMOS (the BIOS memory) before changing any settings in the BIOS, this will be in your motherboards manual and will reset your BIOS settings to defaults.

Before changing any frequencies in BIOS you need to be aware that voltages of value AUTO change to try to force stability. This CAN BE DANGEROUS to your hardware if you don’t have sufficient cooling, please read the following sections before you change anything!

There are some power saving features that have been known to cause problems with overclocking, most people turn off Intel speed step and turbo boost when overclocking.

A quick word on memory; manufacturers sometimes expect you to go into the BIOS and change the voltage and frequency multiplier to achieve the advertised frequency. This can cause compatibility issues if the processor does not support the same voltages as the memory, but for this guide, I will assume you have a working computer.

You will have three different clock frequencies to worry about; CPU, memory and Base Clock [BCLK] (or Front Side Bus[FSB]), the CPU and memory clocks are multiples of the BCLK and therefore this is the only frequency you will see in the BIOS in MHz the rest are likely to be in the form of a multiplier (they might be pre calculated if your BIOS is especially helpful).

Example: say you have a CPU multiplier of 22, a ram multiplier of 6 (2:12) and a BCLK of 172, this would give you a CPU speed of 3784MHz (22*172) and a memory speed is 1032MHz (172*6) note that almost all memory these days is ‘DDR’ this stands for double data rate so you will often see the speed written doubled as 2064MHz, this is why the base clock:memory ratio is sometime written 2:12.

There are many differences (too many to discuss here) between all the different kinds of platforms, however most of the things that you will see will be in some way comparable to what I have written.

With some platforms you may also have a northbridge (controls fast peripherals) multiplier, a HyperTransport (the bus that connects the CPU to motherboard chipset in AMD processors) multiplier and a Quick Path Interconnect (the Intel version of HyperTransport) multiplier. all these will work in the same way as the previously discussed multipliers.

With some chips, like Intel’s unlocked ‘K’ series processors, the Base clock can be left alone.  Overclocking for these chips is somewhat simpler than others because they use an unlimited multiplier for the CPU frequency. With most other chips, the CPU multiplier is locked at a certain value. Example: Intel i7 860 is locked at 22 so if you want to increase the clock higher than 22*133 (the standard base clock for the 1156 platform) = 2926MHz you will have to increase the base clock.

The basic idea is to increase the frequency a little, and test for stability, increase it again and test again, until you see instability in the tests.  Drop the frequency back to the previous value you tested and you have your overclock.

If you are doing this by increasing the base clock, you will be adjusting the speed of your memory as well as your CPU.  You will need to test this and possibly adjust the multiplier down if your memory is becoming unstable and your CPU is still stable (I only say this because most people would choose a higher CPU speed over a higher memory speed because it has far more effect on real world performance.  But if you find yourself having to drop a memory multiplier just to get an extra MHz on your base clock then it might not be worth your while, depending on what your using your computer for).

The whole process is essentially a trial and error process which takes a lot of time (mostly stability testing which I will go through in the next section).

Stability Testing.

This involves stressing the CPU/memory and using a checksum, or some kind of pre- calculation to check the answers it gives to the calculations its doing (basically checking that the longest instructions are going to fit within clock cycles).

Good programs to use:
Prime 95: tests the CPU and in blend mode the memory is tested as well.

IBT: tests both the CPU and memory MemTest: tests the memory

I, and a lot of the people I have spoken to use these three programs in the following way:

IBT on maximum setting for a short amount of time; < 30m as a quick check when increasing the frequency until I see instability here.  I then drop the BCLK/multiplier (whatever I have been increasing) back by one and run Prime 95 and MemTest (you can run these at the same time but bare in mind that MemTest takes up time on a core/thread and this core/thread will be effectively tested for less time), Prime for about 8hrs, MemTest for about 3hrs.

Everybody who overclocks has their own method which they think is best for stability testing, and there is no way to tell that a computer is 100% stable. I have had no notable problems using this method.

Temperature.

One of the biggest things you hear when you mention overclocking is the damage you can cause to your processor.  While there are ways in which voltage can damage your processor, temperature is also of concern.

You should look up the specifications for your processor, you need to look for Tcase which is the maximum temperature that the CPU can withstand as measured on the case.  This should be similar to the Tjunction as measured on each core by a program like HWMonitor

You can find the Tcase of your processor by searching here for Intel processors, and here for AMD processors.

It is a very good idea to keep an eye on your temperatures at all times when stability testing, as this will likely yield the highest temperatures you will see at whichever settings you are running. Its also a good idea to do stability testing at the hottest time of the day or leave headroom for the ambient temperature to change.

Voltage.

Here is where it starts to get a little more complicated; I mentioned before that leaving voltage on AUTO can be dangerous.  This is because if you set a higher than stock clock frequency on your CPU/memory, your motherboard may try and compensate by increasing the voltage (sometimes far more than is needed, sometimes less).

If you are just looking for a small overclock (I don’t want to give a value because it varies dependent on lots of things but say ~5-10% ) then leaving the voltages this way should be fine (but keep an eye on your temperature).

If you are willing to do a little trawling through data sheets you will be able to find the minimum, maximum and usually a typical setting for all the voltages in your platform.  You can set this at whatever you feel comfortable with as long as it keeps the temperature lower than Tcase.

Its a good idea to work your way up, stressing the CPU each time to check it is still cool enough. Note at this point that increasing the voltage will have a quadratic relationship (the temperature will rise faster and faster for every 0.1V you add) with heat.  Increasing the clock, on the other hand, has a linear relationship (the temperature will rise the same amount for each MHz you add), so be extra careful increasing the voltage.

Different voltages will have effects on different things, and there are a multitude of different names for each voltage. I cannot explain all these here as there are so many.

You should see all of these voltages in the data sheet to your CPU or in your motherboard manual and they should guide you as to appropriate values and what they should have an effect on. To use the example of the 1156 platform again, Vcc is the Vcore and has a limit at 1.4V (however you will not get anywhere near this value if you are using stock cooling) Vddq is the memory voltage and has a limit at 1.575V (which means this platform in incompatible with any memory with a higher voltages, not that this stops most people running them).

Vtt is the IMC voltage (Internal Memory Controller) and has a limit at 1.155V. Vccpll is the PLL voltage, this is the part of the processor that allows it to have a higher frequency than the base clock but to still remain in phase with it, this has a limit at 1.89V.

Conclusions.

While reading this guide you will have realised that one of the most important things you are going to have to do is research on your particular CPU.  Because computer systems have so many different limits and dependents I cannot discuss them all here.

I have tried to make this a general guide and have given links to find all the specific information for your CPU. I hope this article has given you a bit of an understanding and a place to start in improving your computers performance.

Author

Matt

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