Which component requires a technician to install screws externally through the PC case?

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Which component requires a technician to install screws externally through the PC case?

  • RAM
  • CPU
  • motherboard
  • power supply

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The correct answer is “power supply.”

When assembling or repairing a desktop computer, the power supply unit (PSU) is the component that requires the technician to install screws externally through the PC case to secure it in place. This step is part of ensuring that the PSU is firmly mounted and aligned so it can safely provide power to every internal component.

Below is a detailed 1000-word explanation about why the power supply requires external screws, how it differs from other components, and the general process involved.

Understanding Why the Power Supply Requires External Screws

The power supply is usually positioned at either the top or bottom of a PC case (depending on the case design). To secure it, the technician must align the PSU with the back panel cutout and then insert screws from outside the case into the PSU’s mounting holes. This is because the PSU must be tightly fixed to prevent:

  • Vibration

  • Noise

  • Movement inside the case

  • Damage to connectors

  • Power instability

Most standard cases and power supplies follow the ATX PSU mounting standard, which requires four screws at the back of the case.

How the Power Supply Is Installed

Here is the typical installation process:

  1. Open the case by removing side panels.

  2. Insert the PSU into the designated PSU chamber inside the case.

  3. Align the PSU fan direction (up or down depending on case airflow).

  4. Match the PSU screw holes with the screw holes on the back of the case.

  5. Install screws from outside the case through the rear mounting plate.

  6. Tighten all four screws for stability.

This makes the power supply the only component in standard PC assembly that is mounted using screws inserted from the outside of the chassis.

Why the Other Options Are Incorrect

1. RAM (Random Access Memory)

RAM modules install directly into motherboard DIMM slots inside the case.
They require:

  • No screws

  • No external mounting

  • Only downward pressure to lock them into the retention clips

RAM uses snap-in retention arms, not screws.

2. CPU (Central Processing Unit)

The CPU installs inside the socket on the motherboard.
It requires:

  • Opening the ZIF (Zero Insertion Force) lever

  • Placing the CPU carefully into the socket

  • Closing the retention lever or locking mechanism

The CPU never requires screws, and certainly not external ones.
Cooling systems (heatsinks or coolers) may use screws or brackets, but all are installed inside the case.

3. Motherboard

A motherboard does require screws, but they are installed from inside the case, not outside.

The motherboard is mounted onto standoffs inside the PC chassis, and screws are inserted from the inside surface of the board downward into these standoffs. No external screws are used.

Motherboard screws are internal because:

  • The board must rest on insulated standoffs

  • Routing ports must align with the I/O shield

  • External screws would misalign components

  • The case structure encloses the board internally

Why Only the Power Supply Uses External Screws

The placement of the PSU at the rear of the case means:

  • The PSU’s metal frame must align with the case’s rear plate

  • The power cable socket and switch must be exposed outside the case

  • Screws can only be inserted from the exterior side

Other components are internal and don’t require this kind of rear access.

The PSU is the interface between internal electronics and external AC power, which explains its unique mounting position.

Mechanical Reasoning Behind External Screws

The PSU is one of the heaviest components in the system. To ensure safety and stability, it must be mounted securely. External screws provide:

  • Direct chassis anchoring

  • Vibration resistance

  • Strong mechanical hold

  • Compliance with ATX standards

Additionally, mounting the PSU with screws on the outside ensures:

  • Better alignment with power cord connector cutouts

  • Reduced risk of internal obstruction

  • Easier removal and replacement

  • Proper airflow direction (top or bottom fan placement)

The external mounting system also allows the PSU to be removed without disturbing internal hardware, making maintenance easier.

Step-by-Step Example of External PSU Installation

  1. Prepare the case

    • Lay the case on its side.

    • Remove side panels.

  2. Insert the PSU

    • Slide it into the PSU bay.

    • Ensure fan orientation matches case airflow.

  3. Align the mounting holes

    • Line up the PSU screw holes with the back plate.

  4. Install screws from outside

    • Use four standard PSU screws (usually coarse-thread).

    • Tighten in a diagonal pattern for stability.

  5. Connect internal power cables

    • 24-pin ATX motherboard power

    • 8-pin CPU power

    • SATA and PCIe connectors

    • Peripherals as necessary

  6. Close case and test

    • Turn on the system

    • Ensure PSU fan and system power function normally

Safety Considerations When Installing a Power Supply

Because the PSU deals with high voltage, technicians must take precautions:

  • Always power off and unplug the PC

  • Allow capacitors to discharge

  • Avoid touching soldered points inside the PSU

  • Use only the correct screws

  • Ensure proper grounding and airflow

  • Do not open the PSU itself (dangerous high-voltage capacitors)

Proper installation reduces the chance of:

  • Short circuits

  • Electric shock

  • PSU malfunction

  • Overheating

  • System instability

Common Mistakes Technicians Make

  1. Using the wrong screws
    Loose-fitting screws cause vibration and noise.

  2. Mounting the PSU upside down
    This restricts airflow and overheats the system.

  3. Not tightening all four screws
    Causes PSU movement and cable strain.

  4. Blocking the PSU fan
    Leads to power failure or thermal shutdown.

  5. Forcing the PSU into the slot
    Wrong alignment can bend metal brackets.

Avoiding these mistakes ensures professional-quality assembly.

Conclusion

The power supply is the correct answer because it is the only common PC component that requires screws to be installed from the outside of the case. RAM, CPU, and the motherboard are all mounted internally, and none of them require external screw installation.

Understanding this is essential for technicians who work with PC hardware, as proper PSU installation is critical for system safety, stability, and performance.