Isn't the atomic part of that sentence referring to that they are changing bits separately, which is a bit inefficient since most architectures simply doesn't a

Isn't the atomic part of that sentence referring to that they are changing bits separately, which is a bit inefficient since most architectures simply doesn't allow that. To set a single bit the writer must read the whole byte, modify it and then write the whole byte back. This is slower than simply writing the whole byte. That is, I don't think they are referring to the same concept of atomicity as you are.