learn to hardware: Functions of the major hardware components in a computer system

The main function of a computer system is to process information. An example operation done using a computer is to create a document. The processing of this information goes through a set of phases, each of these phases require it's own set of devices.

The first phase is the Input phase, where data is entered into the computer system through input devices.
After data is inputted into the computer system, it is then processed and some changes or computations are done by the Central Processing Unit (CPU).
During the time which the document is being modified, the document needs to be stored temporarily in the computer's Main memory for the CPU to access it.
To save the document for future use, it is stored in Secondary Storage.
The document is then outputted to the screen or printed.

Major Hardware components

The major hardware components of a computer can be broadly categorized as:

CPU(CU, ALU)
Main Memory/Immediate Access storage (Primary Storage)
Secondary Storage
Input/Output Devices

CPU

The central processing unit (CPU) is the brain of a computer system. It carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU is made up of the Control Unit(CU) and the Arithmetic and Logic Unit(ALU).
CU: The control unit is a part of the CPU that instructs other parts of the computer system to carry out program instructions.
ALU: The ALU is a a digital circuit that performs arithmetic and logical operations.

Main Memory

Main Memory is a form of Immediate Access Storage also known as primary storage, it is volatile memory directly accessible to the CPU and is used to store data actively operated on. The CPU continuously reads instructions stored there and executes them as required. Information stored in main memory is lost when the computer is powered off.

Different memory chip sizes for different devices

Secondary Storage:

Secondary storage differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfers the desired data using an intermediate area in primary storage. Secondary storage does not lose the data when the device is powered off and it is non-volatile. Secondary Storage Devices Include the Hard Drive, Flash Drive, Memory Card. Secondary storage devices are discussed in depth at http://cleverlogic.net/book/types-secondary-storage-media

Input Devices:

An input device is any peripheral (piece of computer hardware equipment) used to provide data to the computer. Input Devices Include the Mouse, Keyboard, Touch Screen Monitor, Scanner, Track Pad, Microphone, Joystick, Web Camera.

Output devices:

An output device is any piece of computer hardware equipment used to communicate the results of data processing carried out by the computer to the outside world. Output Devices include the Speaker, Printer, Monitor, Plotter.