The Central Processing Unit (CPU) is the heart of your computer as it performs nearlly all
functions that require extensive processing power. Therefore, it is very important that you
choose a suitable CPU for your function as the choice of CPU directly affects the speed and
stability of your system.
Before we can explain differences between CPUs, you must first be familiar with certain CPU
•Clock Speed, measured in Gigahertz (GHz), or Megahertz (MHz) on older systems is the
number of calculation cycles that your CPU can perform per second. Therefore, a higher clock
speed generally points toward a faster system. But not all CPUs perform an equal quantity of
work per cycle, meaning two CPUs at the same clock speed can potentially perform at very
•IPC, or Instructions Per Cycle is the amount of work a CPU can do in a cycle. This varies with
diffrent properties of the CPU.
•Front Side Bus Speed (FSB) is the rate at which the CPU communicates with the motherboard
Front Side Bus components in MHz. A larger FSB value shows that your CPU is able to
communicate with other components on the motherboard (and thus your system) faster.
•Interface: CPUs must connect to motherboards via a series of connectors. It is VERY
important that your CPU interface is a COMPLETE MATCH to your motherboard CPU socket
otherwise you would be wasting money on a piece of spare silicon.
•Bit-Rate: Most modern CPUs are of the 32-bit system which work fine with most modern
operating system and hardware. Higher end models are the 64-bit system which may allow
faster CPU processing capabilities due to the larger band-width, but not all operating systems
are compatible with the newer 64-bit format -- they will still run, but without a major
•Hyper Threading (HT): Hyper-threading is a new technology of parallel processing which
instead of one single core, your CPU is able to have separate cores working on different tasks
which greatly speeds up the system speed. However, Hyper Threading technology requires a
motherboard that supports Hyperthreading technology which are generally very expensive. And
of course the software you use has to be optimized for Hyperthreading to give more speed.
•Manufacture and Model: There are two main manufactures of CPUs Intel and AMD, each
having advantages and disadvantages that would be explained below.
•L2-Cache: the amount of Memory dedicated for the CPU in MB, generally, the larger the L2
cache, the faster your system would run. However, L2 cache uses a lot of transistors, and the
larger the cache, the transistors needed, which consums more electricity, and outputs more heat.
•The Core of the CPU is the heart of the CPU. Often several cores will be marketed under the
same name, so look at what core you are buying.
Now, one of the most common mistakes of choosing a CPU is by ignoring the fine print of
CPU specifications while relying completely on the clock speed. CPUs specs are written in full,
I give a brief explanation of the spec, eg.
Intel Pentium 4 3.2GHz LGA775 FSB800 HT L2-2MB
Model: Intel Pentium 4
Clock Speed: 3.2GHz (=3200MHz)
Interface: Land Grid Array 775
L2-Cache: 2MB (=2048 kB)
Other Spec: HT technology
The consumer logic for processor speed may be misleading because many consumers think that
clock speed, which is measured in gigahertz (GHz) or megahertz (MHz) is equal to system
speed. While the higher the clock speed the CPU is able to do cycles more frequently and it
does have a fundamental effect on speed, it is not the sole factor as the number of calculations
per cycle is different for each different manufacturer and model.
Intel classifies its CPUs using a series of numbers. 3xx, 4xx, 5xx, 6xx and 7xx of which 7xx
being the highest end products. Generally, the higher the number, the faster the CPU and the
more expensive. usually, models and ratings correspond.
•3xx Series: Intel Celeron (L2-128KB)
•4xx Series: Intel Celeron D (L2-512KB)
•5xx Series: Intel Pentium 4 / Celeron D (L2-1MB)
•6xx Series: Intel Pentium 4 / Pentium 4 XE (L2-2MB)
•7xx Series: Intel Pentium 4 XE
•8xx Series: Intel Pentium D
•9xx Series: Intel Pentium D
the number followed by suffix J signifies XD technology
Intel Pentium 4 3.0GHz L2-1MB with HT --> Intel Pentium 4 530J
AMD CPUs are even more confusing in classification. The AMD Athlon CPU rating are NOT
of the actual clock speed but rather the equivalence bench mark performance corresponding to
a comparason to the AMD Athlon Thunderbird 1.0Ghz. The conversion Table is as follows,
AMD Athlon 1500+ = Actually runs at 1.33 GHz
AMD Athlon 1600+ = Actually runs at 1.40 GHz
AMD Athlon 1700+ = Actually runs at 1.47 GHz
AMD Athlon 1800+ = Actually runs at 1.53 GHz
AMD Athlon 1900+ = Actually runs at 1.60 GHz
AMD Athlon 2000+ = Actually runs at 1.67 GHz
AMD Athlon 2100+ = Actually runs at 1.73 GHz
AMD Athlon 2200+ = Actually runs at 1.80 GHz
AMD Athlon 2400+ = Actually runs at 1.93 GHz
AMD Athlon 2500+ = Actually runs at 1.833 GHz
AMD Athlon 2600+ = Actually runs at 2.133 GHz
AMD Athlon 2700+ = Actually runs at 2.17 GHz
AMD Athlon 2800+ = Actually runs at 2.083 GHz
AMD Athlon 3000+ = Actually runs at 2.167 GHz
AMD Athlon 3200+ = Actually runs at 2.20 GHz
In choosing different manufacturers and models, the CPU would generally be dictated by the
way you intend to use your computer. AMD CPUs are generally less expensive than Intel CPUs
of the same clock speed but there are great differences in the CPU architechture. Intel Pentium
4 is specifically designed to optimise clock speed while the number of calculations per cycle is
reduced. Therefore, benchmark tests of the speed of the AMD Athlon XP 3000+ is
approximately the same as Intel Pentium 4 3.2GHz. Most gamers prefer AMD CPUs because
of cheaper price for a faster speed, however, graphic designers and professionals prefer Intel
CPUs due to their Hyper Threading technology.
You may wish to purchase a high end AMD64/emt64 processor, which provides support for
64-bit operating system (eg. Windows XP Professional 64-bit Edition). A 64-bit system is very
efficient in handling large amounts of RAM. A 32-bit system efficiency drops beyond about
512 to 864MB of RAM, and becomes significantly less efficient beyond 4GB of RAM. Most
processors for gaming range in about the 2.8Ghz-3.2Ghz
A 64-bit processor is currently an expensive investment as most applications run on the 32-bit
system. However, there is no doubt that the 32-bit system would gradually be replaced by the
64-bit system when the prices fall over a few years time. It is unlikely that the 64-bit system
would completely replace the 32-bit system within 5 years but Linux users might find a great
improvement in speed when a 64-bit processor is used.
Smaller processors are generally preferred for overclocking, as they run cooler, and can achieve
higher clock speeds. Retail CPU's come in a package containing a HSF (Heat Sink Fan),
instructions, and a warranty, often 3 years. OEM CPUs do not include these.
The current CPU speeds and advantages change frequently, so for up-to-date comparisons, you
may want to check a website that specializes in Hardware reviews, such as Tom's Hardware
Guide or Anandtech. A good, current (as of 14 February 2006) beginner's explanation can be
found at 
CPU cooling is very important and should not be overlooked. A less than average CPU
temperature prolongs CPU life (up to more than 10 years). On the other hand high CPU
temperatures can cause unreliable operation, such as computer freezes, or slow operation.
Extremely high temperatures can cause immediate CPU destruction by melting the materials in
the chip and changing the physical shape of the sensitive transistors on the CPU. Because of
this, never switch on the computer if your CPU has no cooling at all. It is an extremely stupid
thing to do, the scenario of 'I'll just test whether my CPU works!' as by doing so, you would
find that the CPU fries in less than 5 seconds and you will be off to buy a new one.
Most CPU installations use forced-air cooling, but convection cooling and water cooling are
also options. For traditional forced-air cooling, the heat sink and fan (HSF) included in most
retail CPUs is usually sufficient to cool the CPU at stock speed. Overclockers might want to
use a more powerful aftermarket fan, or even try water cooling because they need additional
cooling ability given the increased heat of overclocking.
HSFs with decent performance are usually copper-based. The cooling effect is enhanced if the
HSF has heatpipes. Silent (i.e. Fanless) HSFs are there to provide users a nearly silent cooling.
Many retail heatsink+fan units have a thermal pad installed, which transfers heat from the CPU
to the fan helping diffuse the heat created by the CPU. This pad is usable only once. If you
wish to remove the fan from another CPU so that you can use it on your new one, or need to
take it off for some reason, you will need to remove it, and apply a thermal paste or another
thermal pad. Note that some of the cheaper pads can melt in unexpected heat and may cause
problems and potentially even damage if you are overclocking. In either case, thermal paste is
usually more effective, just harder to apply. If you plan to do any high performance computing,
or removing and replacing the HSF, often thermal paste is suggested. If you are planning a long
term installation a thermal pad is suggested. Non-conductive thermal pastes made up of silicon
are the cheapest and safest.
Silver-based thermal pastes sometimes perform better than normal thermal pastes, and carbonbased
ones perform better still. When applied improperly both can be conductive, causing
electrical shorts upon contact with the motherboard. A thin properly-applied layer will usually
prevent this problem, though some pastes can become runny when they get hot. Users should
also beware that many "silver" thermal pastes do not actually contain any silver metal.
For quiet operation, start with a low-heat (low number of watts) CPU. Processors made by
VIA, such as the VIA C3, tend to produce low amounts of heat. The Pentium M gives
performance that is on par with many of the desktop processors, but gives off more heat than
the Via processors. You can also underclock your CPU, giving up some unneeded performance
for some peace and quiet. Another option is to choose a large copper heat sink with an open fin
pattern. However, true fanless operation is difficult to achieve in most case designs. You can
position a case fan to blow across the heat sink, or mount a fan on the heat sink. With either
choice of fan placement, choose a large and slow fan over a small and fast fan to decrease noise
and increase air flow.
Some low-noise CPU cooling fans require special mounting hardware on the motherboard. Be
sure that the cooling fan you choose is compatible with your motherboard.