Hardware is the physical components of a computer system. These are the actual components of the computer which  we can see and touch (Even if they are inside the computer). Examples include Processor, Ram, Hard-drive, Keyboard, Mouse, Microphone, Speaker etc...

An input device allows the capture of data by a computer. Examples include Keyboard, Mouse, Microphone, Joystick, Keypad, Scanner, Camera, Card Reader,  Graphcis  Digitiser, Sensor etc, Foot Mouse, Tracker Pad. Each input device has been designed for a certain purpose.

An Output device allows the computer to give information back to the user. Examples include Screen, Speakers, Ink Jet/Laser/3D Printer etc...

A storage device is used to hold data examples include Ram, Hard-Drive, USB Drive, Optical Storage devices(CDRWs), Rom. 

Primary storage is our memory which holds data temporarily, these are described as volatile meaning when they lose power the data is lost.

Secondary storage is used to hold data for long term, these are described as non-volatile meaning when they lose power the data is still kept on the device.

Rom is used to hold the startup instructions (BIOS) for a computer. They are held on Read Only Memory so they cannot be accidentally deleted or damaged which would render the computer unusable.

The CPU can be described as the brain of the computer. Its job is to process all data and complete instructions given by the user. For example if you ask a computer to print a document the CPU will instruct the printer to complete the task. A computer appears to be completing many tasks at once for example playing music while you complete homework or surf the internet. However, the Central Processing Unit is only completing one task at a time. The central processing unit uses a quartz clock to control how much time is given to each task. With each second that goes by the CPU processes one piece of data or executes one instruction. The CPU has many very important components: 

• The Arithmetic Logic Unit (ALU); 

• Control Unit; 

• Immediate-access store;

 • Register 

The ALU processes all data inside the CPU. As it name suggests it handles both Arithmetic (mathematical) operations and Logical operations. 

The control unit manages how data is processed by the CPU, it manages how the CPU and other components communicate, for example communicating with a printer or USB device. It executes all instructions provided by programs. It informs the ALU, IAS along with input and output devices how to respond to instructions from a program. 

The Central Processing Unit must have access to data as fast as possible. Each piece of data is stored in the random access memory chip so that the CPU can retrieve data immediately. Each memory location has a unique address assigned to it. Memory is volatile meaning when the device loses power the data is lost.

Is normally used for a specific purpose, where data or control information is temporarily stored. Some registers are used in the fetch-execute cycle while others may be used by the program being executed. Registers are much faster to access because they have to be accessed so often. 

The Fetch-Execute Cycle explains the basic steps the Central Processing Unit takes to process an instruction. There are 5 stages the fetch-execute cycle goes through: 

1. Program Counter 

2. Memory Address Register (MAR) 

3. Memory Data Register (MDR) 

4. Instruction Address Register (IAR) 

5. Arithmetic Logic Unit (ALU) 

There can be many instructions loaded in the computer memory, each one has its own unique number or starting address. It is the program counters job to have the address of the next instruction to be executed. This will initially hold the address of the first instruction to be executed and will increment each time an instruction is executed. 

The memory address register stores the address of where the data is going to or coming from. 

This holds the actual data that is being sent or received from memory. All data from memory to CPU goes via MDR. 

The Instruction Address Register holds the current instruction which is being executed. 

This is memory located within the processor, it holds the frequently used data and instructions. It is located close to the processor so allows the fetch, execute cycle to be carried out more efficiently when running a program.

 The ALU will carry out the logical part of the instruction for example a calculation. It will also compute any logical decisions (If statements).

Clock Speed 

The CPU clock speed is measured in cycles per second. 1 cycle per second = 1 Hertz. A typical desktop computer is extremely quick, running at 3000 million times per second or 3GHz. It is this speed that makes it look as though the computer is completing multiple tasks at once. The faster the clock speed of a computer the more powerful the computer is, the quicker the central processing unit will work. 

Cache Size 

Cache memory has extremely fast access, so sections of a program and its associated data are copied there to take advantage of its short fetch-execute cycle. The use of cache memory can greatly reduce processing time therefore the greater the Cache size the quicker the processing time. 

Number of Cores 

Modern computers speed up their clock speed/processing power by containing more than one processor. Some companies call these CPU’s ‘core’. Therefore a ‘dual core’ device means the computer contains 2 processors, a ‘quad core’ device means the computer contains 4 processors