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The POST is a ROM program that's executed when the computer is first
turned ON. It performs the following functions:
■ Checks the Switch Settings (PC,XT) or the CMOS Memory (AT,PS/2) to
determine what peripheral equipment is connected and sets the
Equipment List bit flags.
■ Checks RAM and writes data to all addresses (required for RAM error
detection) and tests components (DMA, interrupt, disk, keyboard, etc.).
It beeps and/or displays error codes; see POST Error Codes.
■ Performs ROM-Scan to install add-on firmware and initialize add-on
■ Executes the bootstrap sequence to load DOS.
■ Checks CMOS address 0fH (and 40:0072 in the BIOS Data Area) for special
See Also: System Startup Sequence