Which function is performed by the BIOS?

The function performed by the BIOS that is most specifically highlighted in the context of the question is POST, which stands for Power-On Self-Test. This process is crucial as it occurs when a computer is powered on. During POST, the BIOS runs a series of diagnostic tests to ensure that the computer's hardware components, such as the memory, processor, and storage devices, are functioning correctly. If the hardware passes these tests, the BIOS will then proceed to load the operating system.

While the BIOS does also play a role in checking connected devices and initializing hardware, POST is a distinct, critical function that must occur at startup to ensure the system is ready for use. Other roles of the BIOS include configuration and management of hardware settings and providing an interface for the operating system to communicate with the hardware, but these aspects fall outside the specific function of performing the POST at boot time.