The Spectrum had a different design; there was main memory, and the ULA chip (Uncomitted Logic Array) Would read it or it’s own time and generate the display (i

The Spectrum had a different design; there was main memory, and the ULA chip (Uncomitted Logic Array) Would read it or it’s own time and generate the display (it had priority over the CPU as was usual those days of single port memory if you didnt want static like noise). The sound, and just about everything else, was not mapped to memory but through an I/O address space which the Z80 and 8080 (and 80x86 and even AMD64 still have. This address space, pins, chip select, etc were all distinct from main memory - unlike the C64 where everything was memory mapped.