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The KERNAL is Commodore's name for the ROM resident operating system core in its 8-bit home computers; from the original PET of 1977, via the extended, but strongly related, versions used in its successors; the VIC-20, C64, Plus/4, C16, and C128. The KERNAL consisted of the OS routines (in contrast to the BASIC interpreter routines, also located in ROM) and was user callable via a jump table whose central (oldest) part, for reasons of backwards compatibility, remained largely identical throughout the whole 8-bit series.
According to early Commodore 'myth' and reported by author Jim Butterfield among others, the word KERNAL is an acronym (or maybe more likely, a backronym) standing for Keyboard Entry Read, Network, And Link, which in fact makes good sense considering its role. There's also, however, a theory that the word originated as a misspelling of the word "kernel" (= OS core) by some unknown Commodore employee. The (completely different) OS core in the 16/32-bit Amiga series was called the Amiga ROM Kernel, i.e. using the correct spelling of kernel.
For a small example of applying the KERNAL, see Hello world program. The presented code stub employs the CHROUT routine, found at address $FFD2 (65490), to send a text string to the default output device (e.g., the display screen).
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