Functional Units of a computer

• Functional unit is a part of the CPU that performs the calculations, operations called for by the computer program.
• The main components or Functional units of computer are 
  1. Input Unit.  
  2. CPU (Central Processing Unit).  
  3. Output Unit.  
  4. Memory Unit.
• Initially, data is entered by the user with the help of input units and then it is processed by the CPU and output is displayed to the output unit.     

Input Unit

• The input device accepts or reads the information and data from the user, and then it converts to computer acceptable form.
• Input is any device that feeds information into the computer.
• It allows physical transactions from the physical world to the computer.
• Input devices are
  1.  Keyboard
  2.  Mouse
  3.  Joystick
  4.  Track Ball
  5.  Web Camera
  6.  Bar Code Reader
  7.  Magnetic Ink Character Reader (MICR)
  8.  Scanner
  9.  Light Pen
  10.  Digital Camera
  11.  Optical Character Reader (OCR)
  12.  Optical Mark Reader (OMR)
  13.  Microphone

Central Processing Unit

• The CPU is the primary component of the computer and it controls, operates and co-ordinates all the operations inside the computer. It is the brain of the computer.
• Input devices are
  1.  Control Unit (CU)
  2.  Arithmetic and Logic Unit (ALU)

Control Unit

• It controls and coordinates all the activities of the computer.

Arithmetic and Logic Unit (ALU)

• It performs all the arithmetic and logical operations.

Output Unit

• It communicates the result of processing to the external world. It is an electromechanical device. It converts machine representation into a human-readable form.
• The output is any device that takes information from the computer to be read, printed, displayed, or controlled. 
• They are classified into three:
  1. Printers
  2. Plotters
  3. Visual Display Unit

Memory Unit

• These are used to store any type of data and information. It can retrieve when the user or other devices are needed.
• They are classified into two:
  1. Primary Memory (Main Memory)
  2. Secondary Memory  (or Auxiliary Memory)

Primary Memory:

• Primary memory is also known as the main memory and these are used to store the data temporarily on the computer system.
• They are classified into two:
  1. Random Access Memory (RAM)
  2. Read-Only Memory (ROM)

Secondary Memory

• Primary memory is also known as Auxiliary Memory. It is used to store data permanently on the computer system. 
• They are classified into two.
  1. Sequential Access
  2. Direct / Random Access

Sequential Access

• In this case, data will access one after the other or in a sequential manner. Magnetic type is an example of Sequential access.

Direct / Random Access

• In this case, data can be accessed from any location randomly.
• They are classified into two.
  1. Floppy Disk
  2. Hard Disk