Remarks: Maze Walker

Fortunately, BASIC provides the commands POKE and PEEK to directly write and read physical memory addresses. These commands provide a mechanism for subverting the language abstractions of BASIC, giving the BASIC programmer access to the arbitrary memory manipulation available via assembly language opcodes. If computer memory truly consisted only of data and code, as described by the von Neumann architecture, then POKE and PEEK would have limited utility to the BASIC programmer, merely providing a less convenient mechanism than variables for storing data, as well as the somewhat esoteric ability for a program to modify its own code during execution. But the C64 employs a common computer architecture approach of memory-mapped hardware registers. With memory mapping, in addition to the standard memory space that stores code and data, there are memory addresses for hardware registers that directly control the execution of the machine. These special memory addresses include control for input and output devices, such as screens, keyboards, and printers. On the C64, the BASIC interpreter and operating system code that create abstractions such as PRINT's virtual teletype, perform their lowest level operations by writing and reading these special memory addresses. By providing POKE and PEEK, which were not available in the original Dartmouth BASIC [I don't think memory-mapping was common in 1964, so POKE and PEEK would have had limited utility - further BASIC was operating in a time-sharing environment, so you wouldn't have wanted to provide individual programs access to hardware registers anyway - if we want to go into this, it would be wherever we want to introduce POKE and PEEK], Commodore BASIC provides a backdoor by which BASIC programmers can directly manipulate hardware registers that would typically only be accessible to assembly language programmers.

Fortunately, BASIC provides the commands POKE and PEEK to directly write and read physical memory addresses. These commands provide a mechanism for subverting the language abstractions of BASIC, giving the BASIC programmer access to the arbitrary memory manipulation available via assembly language opcodes. If computer memory truly consisted only of data and code, as described by the von Neumann architecture, then POKE and PEEK would have limited utility to the BASIC programmer, merely providing a less convenient mechanism than variables for storing data, as well as the somewhat esoteric ability for a program to modify its own code during execution. But the C64 employs a common computer architecture approach of memory-mapped hardware registers. With memory mapping, in addition to the standard memory space that stores code and data, there are memory addresses for hardware registers that directly control the execution of the machine. These special memory addresses include control for input and output devices, such as screens, keyboards, and printers. On the C64, the BASIC interpreter and operating system code that create abstractions such as PRINT's virtual teletype, perform their lowest level operations by writing and reading these special memory addresses. By providing POKE and PEEK, which were not available in the original Dartmouth BASIC [I don't think memory-mapping was common in 1964, so POKE and PEEK would have had limited utility - further BASIC was operating in a time-sharing environment, so you wouldn't have wanted to provide individual programs access to hardware registers anyway - if we want to go into this, it would be wherever we want to introduce POKE and PEEK], Commodore BASIC provides a backdoor by which BASIC programmers can directly manipulate hardware registers that would typically only be accessible to assembly language programmers.