CBSE Class 3 Computer Science Computer System Notes Set 01

What is a computer?

A computer is an electronic machine that follows the instructions we give it and works very fast. It can do many different jobs: we can write a letter, draw a picture, play a game, watch a video, do sums and talk to a friend far away. A calculator does only sums, a clock shows only time, but a computer can do all these tasks, so it is called a multipurpose machine. Computers come in different shapes such as the desktop computer, laptop and tablet.

Main parts of a computer

A desktop computer has four parts that we see on the table.

1. Monitor: the screen that shows pictures, words and videos.

2. CPU (Central Processing Unit): the box that works like the brain of the computer. It thinks, remembers and controls everything.

3. Keyboard: the board with keys for the letters, numbers and symbols.

4. Mouse: a small device we move to point at, click and choose things on the screen.

The IPO cycle

Every job done by a computer has three steps, which together are called the IPO cycle.

1. Input: the instruction or data we give to the computer. Input means to put in.

2. Processing: the work the computer does by itself on the input. This happens inside the CPU.

3. Output: the result that we get after processing, shown on the screen or on paper or heard through speakers.

Think of making a glass of lemonade. The lemon, water and sugar are the input. Squeezing and mixing is the processing. The lemonade is the output. A computer works in the same way, but with information instead of food.

Input and output devices

The parts used to give input are called input devices. The parts used to receive output are called output devices.

Input devices: keyboard, mouse, microphone (to give our voice), scanner (to copy a page into the computer) and webcam (to take live pictures).

Output devices: monitor (to see), printer (to get a paper copy) and speakers (to hear sounds).

Worked examples

Example 1. Sort these devices into input and output: mouse, printer, keyboard, speakers.
Mouse and keyboard are input devices because we use them to send instructions to the computer. Printer and speakers are output devices because they give us the result.

Example 2. Name the input, processing and output when we type 5 + 3 on a calculator program.
Input: typing 5 + 3. Processing: the CPU adds the two numbers. Output: the answer 8 on the screen.

Example 3. A child types a story on the keyboard and prints it. Name the devices used.
The keyboard is the input device, the monitor shows the words (output) and the printer gives the story on paper (output).

Taking care of a computer

1. Wash and dry your hands before using the computer.

2. Do not eat or drink near it.

3. Press the keys and the mouse button gently.

4. Always shut down the computer properly when you finish.

5. Sit straight and keep your eyes at a safe distance from the screen.

Remember

A computer cannot think on its own. It needs instructions from us, and it does only what it is told. It is fast and does not get tired, but a person must always decide how it is used.

Quick Check Questions