Int 19h                 Bootstrap Loader Service

    Attempts to load the sector at head 0, cylinder 0, sector 1, of a
    diskette or fixed disk into memory at 0:7C00h, and transfer
    control there. This sector usually has an operating system
    bootstrap loader.

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    This interrupt attempts to load the sector at head 0, track 0,
    sector 1, on the first diskette into memory at 0:7C00h. If unable,
    it then attempts to load the sector at head 0, track 0, sector 1
    of the first hard disk. If it is unable to load from either the
    diskette or the fixed disk, it calls Int 18h, which calls the ROM
    BASIC.

    If Int 19h is successful, control is transferred to the first byte
    of the sector, which has been read in at memory location 0:7C00h.
    That is, CS is set to 0 and IP is set to 7C00h.

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    This interrupt is not a substitute for a Ctrl-Alt- Del warm boot.
    This interrupt is the last action performed by the Power-On Self
    Test (POST), which is activated by Ctrl-Alt-Del. If a user program
    attempts to execute this interrupt directly, the machine may lock
    up.

    To correctly reboot within an application program, jump to FFFF:0h
    in memory. That is, set CS to FFFF and IP to 0. This is the same
    process that occurs when the machine is first powered on.
    Following these steps will perform a "cold" boot. To perform a
    "warm" boot using this method, first set the word at location
    0040h:0072h to 1234h. This will simulate the pressing of the
    Ctrl-Alt-Del.

    A cold boot initializes all hardware, tests all hardware, tests
    RAM, then calls Int 19h to load the bootstrap loader. This process
    is performed when the computer is turned on or a hardware reset
    button is pressed.

    A warm boot initializes and tests all hardware but does not test
    RAM. It then calls Int 19h to load the bootstrap loader. This
    process is performed when Ctrl-Alt-Del is typed.

    The sector read from the diskette will in turn read in the rest of
    the operating system. A fixed disk will read in a Partition Table,
    which will then read in the correct operating system.