3.6 Given a scenario, install the appropriate power supply.
📘CompTIA A+ Core 1 (220-1201)
The 20+4 pin connector is the main power connector that links the power supply unit (PSU) to the motherboard. It is sometimes called the ATX power connector because it follows the ATX motherboard standard.
This connector is critical because it supplies all the power the motherboard needs to run the CPU, memory, expansion cards, and other components. Without it, the system will not turn on.
Why “20+4” pins?
- Older motherboards used a 20-pin connector.
- Newer motherboards need extra power, especially for CPUs and modern components.
- To maintain compatibility, power supplies use a 20+4 pin design:
- 20 pins: Standard older ATX connection.
- 4 pins: Additional power for newer motherboards.
You can connect it in two ways:
- 20-pin only → Works for older motherboards.
- 20+4 pins together → Works for modern motherboards.
Think of it as a modular design that fits both old and new boards. The extra 4 pins just provide more stable power to the motherboard.
What does the 20+4 pin connector supply?
The connector provides different voltage rails to power various parts of the motherboard:
| Pin Type | Voltage | What it powers |
|---|---|---|
| Orange | +3.3V | RAM slots, PCIe slots, some chipset circuits |
| Red | +5V | USB ports, some older components |
| Yellow | +12V | CPU (through VRM), PCIe devices, fans |
| Black | Ground | Common return path for electricity |
| Gray | Power OK signal | Lets motherboard know PSU is stable |
| Purple | +5V Standby | Powers certain functions even when computer is off (e.g., Wake-on-LAN) |
| Green | Power On signal | Tells PSU to start supplying power when you press the power button |
Each wire has a specific role, and if any of them fail, the system may not boot or may become unstable.
How to connect it
- Locate the 20+4 pin connector from the PSU.
- Align it with the main power socket on the motherboard.
- Look for the clip that locks it in place.
- If your motherboard only has a 20-pin socket, detach the extra 4 pins.
- Push the connector firmly until it clicks.
Important:
- Never force the connector—it’s keyed to fit only one way.
- Incorrect connection can damage the motherboard or PSU.
Exam Tips
- Know that 20+4 pin = main power connector for motherboard.
- Recognize that 20-pin = older boards, 24-pin = newer boards.
- Understand that it supplies 3.3V, 5V, 12V, standby, and power-on signals.
- Be able to identify the connector in a photo or in a practical lab scenario.
For CompTIA A+ questions, they may ask:
- Which connector powers the motherboard? → 20+4 pin ATX
- What voltages does it supply? → 3.3V, 5V, 12V, etc.
- Can it fit a motherboard with only a 20-pin socket? → Yes, just detach the extra 4 pins
✅ Summary in Simple Terms
- 20+4 pin connector = Main PSU connection to motherboard.
- 20-pin = older boards, 24-pin (20+4) = newer boards.
- Supplies all essential voltages for motherboard operation.
- Can be split or combined to maintain compatibility.
