Int 15h, 21h            Read or Write POST Error Log                     PS/2

    Used internally by BIOS in Power-On Self Test (POST).

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    Read POST Error Log

        Entry   AX = 2100h

        Return  ES:DI = Address of POST Error Log
                BX    = Number of POST error codes stored
                AH    = 00h
                CF    = 0

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    Write Error to POST Log

        Entry   AX = 2101h
                BX = POST 16-bit error code
                     BH = device code
                     BL = device error

        Return  CF = AH = 00h if error stored
                              01h if log is full, error not stored

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    This service is used by BIOS during the Power-On Self Test (POST).
    If errors occur, they are recorded in the POST log. The Power-On
    Self Test is concerned with hardware; there is little of value to
    the applications programmer in this service.