Int 18h                 BASIC Loader Service

    Activates Cassette BASIC.

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    This service transfers control to F600h:0000h, which is the
    location in ROM of the standard BASIC interpreter. This interrupt
    works only on IBM computers. Compatibles do not have BASIC in ROM
    but must instead run a disk-based version of BASIC.

    This interrupt is executed if the Power-On Self Test (POST) is
    unable to read the operating system off a floppy or fixed disk.