BIOSPOST

BIOSPOST stands for Basic Input/Output System Power-On Self-Test. It is the initial diagnostic sequence executed by a computer's firmware when power is applied, designed to verify that essential hardware components are present and functioning before the operating system starts.

During POST, the firmware initializes the CPU, memory (RAM), chipset, timers, and basic I/O controllers, then tests critical subsystems such as storage controllers, graphics, and input devices. It allocates memory, runs memory checks, and checks the boot devices. If POST completes successfully, the system proceeds to the boot manager.

If a problem is detected, POST halts and communicates the error via audible beeps or LED/diagnostic codes, and sometimes on-screen messages. Beep codes vary by motherboard/BIOS vendor; LED code displays and POST code readouts are common on newer boards. The exact meaning depends on the firmware version and hardware.

Historically, POST was part of the legacy BIOS; modern systems use UEFI firmware that still performs POST but can display graphical messages and run a Pre-boot Environment. Some systems support fast boot or silent POST that reduce the amount of testing to speed up startup, while still maintaining essential checks.

After a successful POST, control is handed to the boot device or boot manager, and the operating system load begins. POST codes and behaviors are widely used in troubleshooting hardware issues.