Minecraft wiki entry for Redstone_computers, associated text: Instructions are put in the same place as memory and as the ADDRESS part of the instruction is only four bits, we can only reference memory from 1-16 lines, requiring some clever programming to fit larger programs. Memory is also limited to 16 bytes per program. Values and instructions are essentially the same thing, so if you write an instruction to store it onto a line that previously-stored an instruction, that effectively overwrites the instruction with a value. Accidental execution of values might be a problem, so a STOP command must be used to prevent any errors. This is a whole lot to understand, so good sources are https://www.computerscience.gcse.guru/theory/high-low-level-languages and https://scratch.mit.edu/projects/881462/ <-- really helpful actually. and also don't forget to take both CS and ICT for your IGCSEs.