P ower  O n  S elf  T est
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

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Power-On Self-Test