- Sinclair BASIC can coexist with machine code via SAVE/LOAD with CODE, CLEAR to reserve memory, and USR function to call routines.
- The Z80 memory map on 48K Spectrum: ROM at $0000-$3FFF, graphics RAM at $4000-$5AFF, and the rest is RAM; IY register points to system variables at $5C3A and must not be modified.
- Text output uses RST $10 to print characters; control codes $10-$17 replicate BASIC text commands (INK, PAPER, etc.) and AT takes two arguments.
- User-defined graphics (UDG) are stored at the address pointed by IY+65; you can load custom character data (8 bytes each) into that area.