220-1101 Hardware Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  PWR_LED (Power LED) header

  Why it's wrong here

  The PWR_LED header is designed to power the front-panel power indicator light, typically delivering a low-voltage signal (often +5 V) through a pair of pins to illuminate an LED. Pressing the front-panel power switch against these pins will not complete the ATX power-on circuit, because the LED header does not carry the PS_ON# or standby signal used to wake the power supply. At best, the switch would cause no response; at worst, it could feed a momentary short across the LED's polarity-sensitive pins. The switch's contacts are also latching-type in some cases, unlike the logic-level pulse the power-on circuit expects.

• ✓

  PWR_BTN (Power Button) or POWER_SW header

  Why this is correct

  The PWR_BTN (or POWER_SW) header is the correct interface for the front-panel power button. This header pair is connected to the motherboard's power-on logic; when the button is pressed, it momentarily shorts the two pins together, dropping the connection to ground and signaling the chipset/EC to assert PS_ON# on the ATX power supply, initiating power-on. Unlike the LED header, this circuit is not polarity-sensitive, so orientation of the case wire is irrelevant. The momentary pulse—not a sustained connection—is what triggers the power-on sequence, which is why the case button is a momentary switch designed for this purpose.

• ✗

  RESET (Reset Button) header

  Why it's wrong here

  The RESET header is wired to the reset logic of the platform, which forces a system restart by pulsing the reset signal line on the chipset, typically driving it low to reinitialize the CPU and memory. If the power switch were connected here, pressing it would not wake a fully powered-off system from S5 (soft off), because the reset signal is gated and only acts when the system is already powered on. In an active system it might cause a reboot, but it cannot complete the ATX power-on sequence. The power button's function is to toggle the system state, whereas reset only reinitializes the running hardware.

• ✗

  SPEAKER header

  Why it's wrong here

  The SPEAKER header provides a raw, unamplified connection to the internal piezo or magnetic chassis speaker, driven by the motherboard's POST code beep signals. It is an output-only path from the super I/O or EC to the speaker, so it lacks the inputs and circuitry needed to detect a button press. Connecting a power switch here would neither send a valid power-on signal nor register the press; the switch would appear as an open circuit to the speaker driving line. Using this header for the power button would also prevent essential beep-based POST diagnostics from being heard.

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