Memory Cells and Hardware Registers
The address locations POKEd to or PEEKed from may refer either to ordinary memory cells or to memory-mapped hardware registers of I/O units or support chips such as sound chips and video graphics chips, or even to memory-mapped registers of the CPU itself (making possible the software implementation of powerful machine code monitors and debugging/simulation tools). As an example of POKE-driven support chip control, the following POKE command is directed at a specific register of the Commodore 64's built-in VIC-II graphics chip, which will make the screen border turn black:
POKE 53280, 0Pre and non-PC computers usually differ as to the memory address areas designated for user programs, user data, operating system code and data, and memory-mapped hardware units. For these reasons, PEEK functions and POKE commands are inherently non-portable, meaning that a given sequence of those statements will almost certainly not work on any system other than the one for which the program was written.
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