Strand 3: IT Systems

3.1 Hardware

CPU, Microprocessor and Clock Speed



The CPU (Central Processing Unit) is the brain of the computer, it carries out the instructions of a computer program it is also the part that does the computer's main functions. This term started being widely used throughout the computer indusrty since 1960. The design of CPUs have changed dramatically since the first examples, but their basic function is still the same. Originally they were designed for specific purposes in special computers, however now they are mass produced and are programed to do many things. The basic purpose of a CPU is to carry out the instructions on it, the instructions are a series of number and are called a program. The four steps that almost all CPUs use in order to function are fetch, decode, execute, and writeback.

Fetch- This is the retrieving of an instruction which is made up by a number or sequence of numbers from program memory. The location in program memory is determined by something called a program counter (PC). The program counter keeps track of the CPU's place in the current program.

Decode- The decode step is when the instruction taken of the program memory and broken down into bits that are comprehendable by other parts of the CPU. In the number that is fetched there is something called an opcode, the opcode tells the CPU what to do. The remaining bits of the number or sequence are to help with this instruction.

Execute- During this step different parts of the CPU link up so the instruction can be executed.

Writeback- This stage is where the results of the execute step are written to some form of memory which can be then linked to another insruction or some types of instructions can manipulate the program counter instead of directly producing results.

After all of the steps have been complete the process is then repeated for the next instruction.

Here are some examples of the steps when you click to open a file:
Fetch-When you click on the desktop icon of a folder to open it the CPU retrieves a series of numbers of the PC
Decode-The numbers are then broken down and the computer determinds that you have clicked on the file.
Execute-Different parts of the CPU link up so that the folder can be opened
Writeback-The folder is then opened and the CPU waits for you to click again. Once you click again the whole process is completed.


Ever since the introduction of microprcessors in the 1970s CPU have changed greatly, from their design to the way they work. A microprocessor has the same functions of a CPU and it is basically the engine of your computer, most microprocessors are programed to add, subtract, compare two numbers and fetch numbers. All of these functions are part of the instructions that are built into the microprocessor. When your computer is turned on the microprocessor gets an instruction from the BIOS (basic input ouput system), which is stored on the computers memory, this is an example of a program driving a microprocessor. Microprocessors can be found in other devices like printers and electronic calculator. Currently there is no difference between a CPU and microprocessor, infact in some cases the CPU is housed in the same package as the microprocesor.


Clock Speed (Determines the speed of the microprocessor)

Clock speed or clock rate is the number of pulses made by an oscillator which sets the tempo for the microprocessor clock speed is normally measured in megahertz (MHz) or gigahertz (GHz). The clock speed is determined by a quartz crystal system which is also used in radio communications equipment. Clock speed is basically the measure of power that the computer has but this doesn't neccessraly mean your preformance will increase. The average clock speed for computers now is between 1.6 GHz and 2GHz.