System Unit Parts – JSS1 Computer Hardware & GSM Repair Lesson Note (Second Term)

The system unit is the metal or plastic box that holds the main parts of a computer, including the motherboard, CPU, RAM and power supply.

Behavioural objectives

1. State what the system unit is.
2. Name the main parts inside the system unit.
3. Explain the job of the motherboard, CPU, RAM and power supply unit.
4. Explain why RAM loses its contents when the computer is switched off.
5. Explain why the CPU needs a fan or heat sink.

What is the system unit?

The system unit is the case that protects and holds the electronic parts that make a computer work.

• Also called: the computer case or tower.
• Inside it: the motherboard, CPU, RAM, power supply, storage drive and fans.
• Outside it: the monitor, keyboard, mouse and printer connect to it with cables.

What are the main parts of the system unit?

The four main parts of the system unit are the motherboard, the CPU, the RAM and the power supply unit.

What is the motherboard (the big map)?

The motherboard is the large circuit board that connects all the parts of the computer together.

• Picture it: a big city where roads join all the houses. The motherboard is those roads.
• Colour: usually green, but some are blue or black.
• What it does: it lets the parts of the computer pass information to each other.
• What connects to it: the CPU, RAM, storage drive and ports for the keyboard, mouse and screen.
• Why it matters: without it, the CPU could not send instructions to the other parts.

What is the CPU (the brain)?

The CPU, or Central Processing Unit, is the small chip that carries out instructions and does the calculations in a computer.

• Where it is: a small, square chip fixed in a socket on the motherboard.
• What it does: it does the thinking and the maths. When you type a letter or play a game, the CPU follows your instructions.
• Heat: the CPU works hard and becomes very hot.
• Cooling: a fan or a metal heat sink sits on top of it to take the heat away.
• If cooling fails: the computer may slow down, shut itself off or get damaged.

What is RAM (the short-term memory)?

RAM, or Random Access Memory, is the memory that holds the work and programs the computer is using right now.

• Picture it: the top of your school desk. You put the books and pens you need on it so you can reach them quickly.
• What it does: it keeps the letter you are typing while you work on it.
• Where it is: it fits into slots on the motherboard.
• Temporary: RAM is volatile. Everything in it disappears when the power goes off.
• Lesson: save your work often. Saving moves it from RAM to the storage drive.

What is the Power Supply Unit (PSU)?

The Power Supply Unit is the part that changes electricity from the wall socket into the power the computer can safely use.

• What it does: it sends electricity through wires to the motherboard, the storage drive and the fans.
• Conversion: it changes the alternating current (AC) from the socket into the direct current (DC) the parts need.
• Cooling: it has its own fan to stay cool.
• Where to find it: at the back of the system unit, where the power cable plugs in. Many have an On/Off switch there.
• Nigerian note: sudden power cuts can make unsaved work in RAM disappear.

What other parts are inside the system unit?

Besides the four main parts, the system unit holds storage drives, expansion cards and fans.

• Hard disk drive (HDD) or solid-state drive (SSD): stores files and programs permanently, even when the power is off.
• Optical drive: reads CDs and DVDs, found in some older computers.
• Graphics card: helps to produce the pictures shown on the screen.
• Sound card: produces sound for speakers or headphones.
• Cooling fans: move air through the case to keep the parts cool.

What is the difference between RAM and a hard drive?

RAM holds work in use and is erased when power goes off. A hard drive keeps files for a long time.

Summary table: who does what?

Evaluation

1. What is the system unit?
2. Write the full meaning of CPU and RAM.
3. Which part may be failing if the CPU becomes too hot?
4. Why does your work disappear if the computer turns off suddenly?
5. State two things the power supply unit does.

Assignment

Observation task: in the computer lab, look at the back of the system unit. Find where the power cable goes in. Draw this part and write two sentences on what it does.