A Computer System is a Combination of Central Processing Unit (CPU) and Memory
A computer system can process data, pictures, sound, and graphics. They can solve highly complicated problems quickly and accurately. It is because every computer has a central processing unit and storage unit. Where information at first entered in the input unit (IU), then it processed through the storage unit to the central processing unit (CPU) and again CPU through to the storage unit. At last the information or results out from the output unit.
Here is a diagram showing how does the computer system work to make raw data into information/ results.
Describing the major components of the Computer System:
- Input Unit
- Output Unit
- Storage Unit
- Central processing unit
1. Input unit
Some input devices are mouse, keyboard, joystick, image scanner, webcam, graphics tablet, microphone, etc. Input devices functions are:
- It accepts the raw data and instructions from users.
- And, it converts raw data into a machine-understandable form.
- Similarly, it supplies converted data to the computer system for further processing.
2. Output unit 
Some output devices are a monitor, printer, a visual display unit (VDU), etc. Output devices functions are:
- It received finished data from computer systems.
- It covers finished data into the human-understandable form.
- Supplies finished results in the outside world.
3. Storage unit
The storage unit of the computer holds data and instructions and saved them to later use. The storage unit has two types:
I. Primary memory (main or volatile memory)
Primary memory stores and provides speedy information. The primary memory is temporary. The data is lost when a computer is switched off. To store data permanently secondary memory is required. The cost of primary memory is more compared to secondary memory.
II. Secondary memory (Auxiliary or Non-volatile memory)
At first, the information is transferred to primary memory and after to the secondary memory. The secondary memory is slower and cheaper than s=primary memory. Some of the commonly used secondary devices are HARD DISK, CD, pen drive, etc.
Difference between the primary memory and secondary memory of the computer system:
| Primary memory | Secondary memory |
| It is a semi-counter memory. | It is a magnetic and optical memory. |
| The primary memory has a high cost and small size. | Secondary memory has a low cost and large size. |
| This memories storing capacity is small compared with secondary memory. | This memories storing capacity is enormous. |
| Also, it is called volatile memory because it is not transferable with other systems or devices. | Similarly, it also called non-volatile memory because it is transferable with one or more devices. |
3. Central processing unit (CPU) 
The control unit (CU) and the arithmetic logic unit (ALU) of the computer together known as the central processing unit (CPU). It is the brain of the computer. Like a brain it performs the following functions:
- It performs all calculations.
- Also, it controls all units of the computer.
- Similarly, it takes all decisions, etc.
The central processing unit is a combination of CU and ALU.
I. The arithmetic logic unit (ALU)
All calculations are performed in the arithmetic logic unit (ALU) of the computer.
It also does a comparison and takes the decision.
The ALU can perform a basic operation such as addition, subtraction, multiplication, division, etc, and logic operations via >, <, =, etc.
II. Control unit (CU)
It acts as a nervous system for the computer. Also, it controls all other units in the computer. And, the control unit instructs the input unit. Where to store the data after receiving it from the user. Similarly, it controls the flow of data and instructions from the storage unit to the ALU.
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