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IT Support & Hardware · Foundational

Power-On Self-Test (POST)

Firmware diagnostics run at startup that check the CPU, memory, video, and other core hardware.

Definition

POST verifies essential hardware before handing off to the boot loader. Failures are reported with beep codes, diagnostic LEDs, POST code displays, or on-screen messages. A system that powers on but fails POST usually has a CPU, RAM, GPU, or motherboard problem.

Example

Two short beeps or a red DRAM LED during POST indicates a memory problem on many boards.

Exam tip

No POST with fans spinning: check RAM seating, CPU power, and the GPU first.

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