System Unit of computer

The parts of computers which are inside the System Casting are collectively known as System Unit. The system Unit of a computer contains all the important components. Some important parts of the System Unit are Motherboard, Microprocessor, Primary Memory and Power Supply Unit.

a) Motherboard
Motherboard, the printed circuit board (PCB), is the main circuit board in a computer. Motherboard contains computer chips and other electronic components which give function to a computer. Motherboard also contains a microprocessor, ROM, RAM slots, cache memory, keyboard interface, the timing circuits, the real time clock circuits, disk drive interfaces, and the expansion slots. These all components are connected through the use of traces or electric pathways. The pathways that carry data on the motherboard are called buses. None of the other circuit cards (daughter board or expansion board) can work without the motherboard. One can insert an expansion board like sound card, 3D-graphic card, TV card in the expansion slot in order to expand the computer’s capability. The motherboard is also called the system board.

b) Microprocessor
Microprocessor is an integrated circuit formed on a single chip. Each microprocessor has a fixed set of operations (i.e. instruction set) what it can perform. The instruction set of a microprocessor contains all the commands or instructions that it can understand and work on. A microprocessor executes instructions and carries out arithmetic and logical operations. So, it is known as the brain of the computer. The speed of a computer depends mainly upon its microprocessor. The microprocessor has three main parts.

1. Control Unit (CU)
2. Arithmetic Logic Unit (ALU)
3. Registers

All these work together to process the computer’s data.

• The Control Unit Controls the working of all parts of a computer. Control Unit controls the movement of data inside as well as outside the CPU. Control Unit communicates between registers and the ALU and between the CPU and the all the input, output and storage devices. Control Unit directs all the parts of the computer system to perform their tasks.
• The Arithmetic Logic Unit (ALU) performs all arithmetic operations like addition, subtraction, multiplication, division and logical operation like greater than, less than, not equal etc.
• Registers are small memory units used to store immediate data, instructions and result while processing data.

c) Primary Memory
The primary memory (Main Memory) is the internal memory of a computer. Primary memory is a semiconductor-based memory which is on the motherboard of the computer. Primary memory operates at high speed and can communicate directly with the CPU. There are two types of primary memory.
i. Read Only Memory (ROM)
ii. Random Access Memory (RAM)

d) Power Supply Unit
Since a computer is an electronic device it needs electric power to run. The power drawn from the mains is not directly supplied to the parts of the computer. A system unit consists of a power supply unit which is called SMPS (Switched Mode Power Supply). A SMPS of a computer converts the AC input of 220 volts into DC output of ± 12, ± 5 and ± 3.3 volts and supplies the required voltages through cables to the different parts of the computer like keyboard, motherboard, disk drives, etc.