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The true heart of your computer is the CPU (Central Processing Unit or processor). CPUs are classified (and priced) by speed and functionality so it is important to understand the features, so you can make an informed decision about which one you want in the PC system you build. Obviously for a gaming PC or workstation PC you'll want a faster processor, and inversely for a home PC built for simply surfing the web and checking your email you can settle for a more garden variety processor and put that money elsewhere.

CPU or Processor

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 properties.

Clock speed

• 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 different levels.

IPC

• IPC (instructions per cycle) is the amount of work a CPU can do in a cycle. This varies with different properties of the CPU.

Front Side Bus speed (FSB)

• Front side bus speed is the rate at which the CPU communicates with the northbridge chipset component on your motherboard 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 (Socket/Slot)

• 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 performance boost. You will require 64-bit if you require to manage more than 4GB of RAM.

Cores and Hyperthreading (HT):

Dual-Core Advantages

Dual-core processors are a fairly new innovation built by both major processor manufacturers (Intel Core Duo / Core 2 Duo and AMD Athlon 64 X2).

• Multitasking: Each processor has two processing centres (cores) for (a theoretical maximum of) twice the operating power and for better multitasking. Major advantages of dual core processors are evident when doing heavy multitasking, such as encoding video and playing video games at the same time.
• Application Support: Newer applications are being written to take advantage of this technology by using a technique known as Multithreading. o Power Saving: Dual core processors (especially Intel Core Duo) have the ability to turn off one of its cores when application demand is low to save power.

Disadvantages

• Support: Older programs (with certain notable exceptions) do not support multithreading and may run slower on dual core CPUs.
• Price: Dual core processors are also significantly more expensive than their single core brethren

Multi-core Future?

However with quad core technology around the corner, and more and more programs being built to take advantage of multiple cores, the prices are sure to decrease, and the availability and usability of dual core processors is sure to increase greatly.

Hyper-threading (HT)

Hyper-threading is a technology which allows a single core processor to simulate having two cores, giving a performance boost when running several programs at once. It requires motherboards and chipsets supporting Hyper-Threading technology. It also suffers similar disadvantages as Dual-Core Processors of support and price.

Cache

Cache is the amount of Memory dedicated for the CPU in MB. Generally, the larger the cache, the faster your system would run. However, cache uses a lot of transistors, and the larger the cache, the higher number of transistors needed, which consume more electricity, and output more heat. Cache comes in (usually) three varieties, L1, L2, and L3. L1 being the smallest and fastest, and L3 being the largest and slowest. Usually only the L2 cache size will be shown, as L3 is rarely used in processor design, and L1 will often stay the same size throughout an entire processor product line.

Core

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. For example:

• 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)
• Frontside Bus: 800 Mhz
• 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 comparison 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

You may wish to purchase a high end AMD64/EM64T (from Intel) 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. Note that there are processors that can run 32-bit code and 64-bit code; they are becoming very popular and may prove a very wise investment for the future of computing, which will invariably be 64-bit. They are more expensive than processors that only run 32-bit code; however, it should be noted that AMD has invested in this market faithfully, and therefore all of their processors, even their low-end Sempron line, runs both types of code. The same cannot be said for the Intel family, which only includes such technology in their high-end server processors and the majority of their desktop line in what is called "EM64T", or Extended Memory 64 Bit Technology. This is an advantage to purchasing an AMD processor.

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 current beginner's explanation can be found at Behardware.

AMD Athlon 64 processor 3200+ Socket 939 ( ADA3200BPBOX )