Can modern x86 hardware not store a single byte to memory?
TL:DR: On every modern ISA that has byte-store instructions (including x86), they’re atomic and don’t disturb surrounding bytes. (I’m not aware of any older ISAs where byte-store instructions could “invent writes” to neighbouring bytes either.) The actual implementation mechanism (in non-x86 CPUs) is sometimes an internal RMW cycle to modify a whole word in a …