What is a CPU / Central Processing Unit / Processor ?

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What is a CPU?
A Central Processing Unit, also known as a CPU, it contains electric circuits which execute programs. CPU’s have been in use since 1961 and have since developed as a main-stream computer hardware product, when it was first developed it was made as a “one-of-a-kind” piece of hardware, however when Computers started to become a more popular CPU’s started to be developed on a large scale.

In the 1970’s Microprocessors were introduced with the first one been the Intel 4004, However it wasn’t until 1974 that microprocessors came into mass production with the Intel 8080. A Microprocessor is a processor on a microchip, sometimes called a logic chip. They are much, much smaller to the original CPU developed in the 1960’s and is a lot faster. A Processor does 4 main functions; Adding, Subtracting, comparing and moving numbers from one area to the next.

How does a CPU work?
A CPU usually takes 4 main steps when doing any functions, these steps take only a few milliseconds.

The first step of a CPU’s functions is to fetch the instructions from the program memory, these instructions of course are represented by a sequence numbers. The location in the Program Memory is set in the Program Count (PC), the PC stores a number which relates to the current position in the memory so that the CPU knows what place it is in the program.

The second step is to decode the instructions provided to the CPU from the Program Memory, these instructions are broken up into parts so that the CPU can understand them, usually one group of numbers in the instructions is called the “opcode”, other than the opcode the remaining parts of the instructions contain the details, these details could be things like grabbing data from the memory.

The next step is to execute the instructions provided to the CPU, this requires the CPU to make connections in order to do a function. For example if an addition or subtraction function is started then the CPU will make a connection to the ALU (Arithmetic Logic Unit) providing it with the inputs (e.g. 2 and 2), the ALU will then process the operation and provide the CPU with the output (e.g. 4). Sometimes the output from a connection is too large, this requires the output to be stored in registry.

The final step simply sends the result of the execute step to a memory address, this is usually inside the CPU for quick access, however they can be stored in the RAM which is a lot slower but cheaper.


What are the parts or a CPU?
The CPU contains several parts, all having there own purpose and functionality.

Control Unit (CU)
The control unit is like the brain of the CPU, it controls the connections between different areas of the CPU and computer.

Arithmetic Logic Unit (ALU)
The Arithmetic Logic Unit is used to calculate data sent from the CPU, it does this via a complicated set of logic circuits and accumulators.

CPU Registers
The CPU registers are basically temporary memory used by the CPU during the execution of instructions. There are several types of registers in the CPU:

Instruction Decoder
This Register simply decodes the instructions before execution.

Program Counter
The PC stores the location of the next instruction to be executed.

Instruction Register
This IR stores the instructions been executed.

This ACC stores the result of calculations done by the ALU.

General Memory
This Register simply stores any remaining data from the instructions been executed.


What CPU to purchase?
Of course with every product you buy you need to ask yourself “What will I be using it for?” and “What is my budget?”, CPU’s come in a wide range of types, speeds and most importantly prices.

Dual Core
Dual Core Processors are simply multiple CPU’s in one single chip. Duel Cores are of course better than single core processors however they usually cost a lot more, like I said earlier it depends on what you plan to do, If you plan to simply browse the web then a Duel Core processor may not be needed, however if you want to play games or run video-editing software then a Duel Core would improve the performance of your PC. However its not as simple as that, in order for the multiple cores to be used the applications/games your running must have the ability to use them. Please note that Duel cores will increase performance for most users as the second core is also used by Windows.


Processor Speed
Also known as Clock Speed, CPU’s can range when it comes to the speed that they run at, this speed is presented using GHz, a low end CPU could run at 1.86GHz, where as a higher end CPU would run at 3GHz.

Everyone can only buy what they can afford, so price is a very important factor when purchasing a CPU. A Intel Celeron D 347 can be purchased for only £30, however the performance will be A LOT lower compared to a Intel Quad-Core Xeon E5440 which costs £570.


I am now going to finish by comparing two CPU’s. The two CPU’s that I am going to compare are the:

Intel Core 2 Quad Q9400
Intel was founded on July 18th 1968 and has since been creating multiple types of processors worldwide, they also make a wide range of other hardware. Intel is well known for creating high quality processors and is currently the world’s largest producer of processors with revenue of 37.6 billion dollars and over 83,500 employees.
The Intel Core 2 Quad Q9400 costs around £192 and consists of 4 cores (hence the name “quad core”). This processor is slightly more expensive than most on the market, however its performance makes it well worth the investment. It has a clock speed of approx 2.66GHz and 4MB (Level 2) cache, as you will notice it has a slightly lower clock speed than the AMD, however due to it being a quad core the performance of running multiple tasks is much higher. The Intel Q9400 will only work on motherboards with LGA 755 sockets (also know as Socket T). Due to the wide range of processors that use the LGA 755 sockets, the Intel Core 2 Quad Q9400 can be very easily upgraded to other Intel chips.

AMD Athlon 64 X2 Dual Core 7750+
AMD is slightly older than Intel and was founded in 1969 and is not as big as Intel with revenue of nearly 6 billion dollars and only 14,700 employees. AMD have been known for creating a more affordable range.
The AMD Athlon X2 Duel Core 7750+ costs nearly £50 and consists of only 2 cores. It has a clock speed of approx 2.70GHz and 3MB (Level 2+3) cache. The AMD Athlon 7750+ will only work on motherboards with AM2+ CPU Sockets.

Of course it depends on what type of person you are and what resources you have available to you, however overall I think the AMD Athlon 7750+ is much better value for money and would fit well in most circumstances. Intel is famous for processors, but I think this time AMD has out done itself by providing a decent processor at nearly ¼ of the price. Both processors use technology to reduce the noise and heat resulting in a more eco friendly processor.

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