Cheap Computer CPU and how it works

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Your cheap computer CPU (Central Processing Unit) is the 'brain' that controls the internal activities of your computer.

Just like the human brain processes information and directs the body to perform certain actions, it processes instructions and directs the operations of the computer.

The CPU may also be called the Microprocessor or the Computer Processor

By whatever name it is called, it is the component that actually does the 'thinking'. All the other parts of the computer are designed around it.

The processor isn't just a very important component of the computer; it's crucial! Without one, the system couldn't perform. In other words, a computer system without a CPU, would be like a car without an engine -It simply wouldn't perform at all!

The reliability of your computer system is determined by the quality of your computer processor. The type of motherboard that you use would be determined by your choice of processor.

You can browse here for a wide range of cheap computer CPUs. icon

The microprocessor consists of three basic sections:

  1. The ALU (Arithmetic Logic Unit).
  2. Registers.
  3. Control Unit.

Internal Schematic of a CPU

Inside a CPU

Today's CPUs have more complex configurations but this is just caused by major modifications to the three basic sections. The outcome is an extremely efficient computer cpu.

These three sections of the microprocessor work together to control the operations of the system. They are connected to the system bus and handle the input, output and storage of data.

Let's examine the three sections of the microprocessor in more detail:

ALU (Arithmetic Logic Unit) - This unit performs the computing functions involving integers (whole numbers).

  • Arithmetic operations which include addition, subtraction, multiplication and division.
  • All logic operations which involve comparisons such as less than, greater than, or equal to.

All information in a CPU is reduced to a numeric function; therefore, the ALU is constantly handling arithmetic and logic operations.

The results of these operations are stored in the registers or in memory or sent to output devices.

Registers - All data is temporarily stored in registers during the execution of programs and the size of the internal register determines how much information the CPU can process at one time.

Control Unit - This unit handles the timing and control signals to all the operations in the system. You can compare the control unit to a police officer directing traffic at a busy intersection; but, instead of directing cars, the control unit directs data flow between the computer processor, memory and peripherals.

This basically wraps up the functions of the three sections of the CPU.

You can check out my guide to installing the Computer Processor and Heat Sink/Fan Assembly here.

There are some other terms you will need to become familiar with before continuing, such as:

System Bus:

The CPU transfers data to other components in the system through the system bus. There are two types of bus regularly referred to:

  • The Front-Side Bus (FSB) carries data between the processor and the Northbridge chipset.

  • The Back-Side Bus (BSB) connects the CPU to the cache.

The system bus or processor bus is an external data bus. External data bus describes the wires and traces on the motherboard that are used to send and receive data.

The greater the amount of traces (bandwidth), the more data you can send and receive. Bandwidth is referred to as the maximum theoretical throughput of the front side bus (FSB). In the first set of PCs, the bus was 8 bits wide, meaning that 8 bits could be transferred at the same time. (In the binary numbering system, a bit is a single digit, either a '1' or a '0'. A combination of 8 bits is called a byte).

Systems advanced and a faster rate of processing more data became necessary. As this need for faster processing of data increased, the bus width was expanded to 16 bits, then to 32 bits and then to 64 bits. A 64-bit bus can carry eight times as much data as an 8-bit bus. Today's systems utilize a 64-bit technology.

With advances in technology, CPUs capable of handling extremely large amounts of data are manufactured. Therefore, the buses had to be widened to facilitate the movement of huge amounts of data being processed hence the use of 64-bit technology.


A cache is a small amount of high speed memory provided to hold data. Some CPUs have cache which vary from 2MB to 12MB of static RAM (SRAM). Static ram performs much faster than dynamic RAM (DRAM) which is used for the system's main memory.

Present processors are equipped with L3 cache. Some examples of these are the Intel Core i7 and the AMD Phenom II X6 chips.

The data requested by the CPU, is handled by the cache controller. The cache controller may be built into the processor or it may be built on the motherboard. Overall, cache dramatically increases the speed at which the computer processes data.

Because this cache is internal, it can be accessed directly and keeps up with the speed of the microprocessor. Without this cache, the microprocessor would have to wait for the data to come from the main memory.

In these present powerful chips, there are now billions of transistors. This is made possible because of the process technology used to miniaturize these internal components.

Processing has come from 90nm to 65nm to 45nm and now 32nm achieved by Intel.

Math Co-processor:

The Math co-processsor (also called the FPU or floating-point unit) handles decimal calculations. In computer language, these calculations are called floating-point math. These calculations slow down the processor but if a math coprocessor is present, it performs these operations much faster.

You have now learnt about the basic internal components of a computer processor. Let's go further and take a look at how it functions.

How does a CPU Work?

The basic operation of a CPU is to execute a sequence of stored instructions known as a program.

A program is represented by a series of numbers that are retained in the computer memory.

To execute a program, the CPU performs four (4) basic steps; namely fetch, decode, execute and writeback.

  1. Fetch - In this first step, instruction is retrieved from memory. Fetching the instruction from memory can be slow and causes the processor to stall while waiting for the instruction to return. This problem was obvious in older CPUs but in newer processors it was corrected by the incorporation of cache.

  2. Decode - In this step, instruction is divided up into portions that are significant to other parts of the CPU. The processor's instruction set architecture (ISA) interprets this numerical instruction value.

  3. Execute - During this step, various parts of the processor are connected to perform a required operation. For example, if an addition or a subtraction operation was required, the arithmetic logic unit (ALU) would be connected to a set of inputs and outputs. The inputs are the numbers that will be added or subtracted and the outputs would be the final sum.

  4. Writeback - The last step does exactly what it is called......writes back the results of the execute step to computer memory. Most times the results are written to the processor's internal register for quick access by the next set of instructions.

    After the instruction execution and data writeback, the entire process repeats.

Let's add a little more to the above information:


This is the process by which external data is received into the computer. This could either be running a program or getting keyboard responses. Common inputs include a keyboard, mouse, modem, scanner, etc.

The computer system analyzes the input data.


Process describes the converting of input into output and is generally guided by a program.


Output is the process by which the CPU sends data to devices such as the monitor, printer, disk drive, etc. Output takes the results of the processing and sends them to be stored in memory or printed or displayed.

Output is the final result of the processing of the data that was input and used by the computer system.

Data must be stored either temporarily or permanently. Therefore, this is where memory is required. The computer needs a way to hold onto data as the processing is being performed.


The computer stores data in memory and retrieves the data it needs from memory. There are two kinds of memory - ROM and RAM.

ROM (Read-Only Memory) is permanent and will be retained even when the computer is turned off - eg. BIOS.

RAM (Random Access Memory) is volatile and data stored in RAM will be erased when the computer is turned off. The processor uses RAM to store data and retrieves data from RAM as it's needed. The instructions of a program, for example, would be stored in RAM. RAM will be lost if the computer loses power.

CPU Limitations

Having described the computer processor and how it works, we now need to know its capabilities and limitations.

CPU Cooling

Very little power was consumed by the earlier processors but today's 'power-hungry' CPUs consume much more power. Some are built for energy efficiency.

Processors will crash or malfunction if overheated; therefore, it is of utmost importance that they have adequate cooling.

The two main methods of CPU cooling are liquid and air cooling of which the latter is more widely used. Liquid cooling is now provided by many PC manufacturers and is undoubtably the more efficient.

In both types, the heat sink or heat sink/fan assembly must be securely mounted to the processor after applying thermal compound to the core. Thermal compound assists in the fast dissipation of heat from the CPU.

EXERCISE EXTREME CAUTION when installing the heat sink since improper installation can damage the CPU or motherboard.

Substandard cooling can cause maximum operating temperatures to be exceeded. This may or may not damage the CPU but could cause crashes in processors. This malfunction generally disappears when the processor cools down.

In the case of Intel, if it overheats, it will automatically reduce its speed thus avoiding damage. Sometimes this reduction in speed goes unnoticed.

If you operate the processor without a heat sink, some CPUs will generally be permanently damaged unless the motherboard is equipped with special protection circuitry.

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