> Perhaps this is layman's understanding, but afaik all CPU operations are only done on registers, so any variable has to be moved to registers when it's operat

> Perhaps this is layman's understanding, but afaik all CPU operations are only done on registers, so any variable has to be moved to registers when it's operated on From the CPU point of view, yes, but many instructions set architectures (including the very common x86 family) have instructions in which one of the operands can be either a register or a memory location. When it's a memory location, the CPU will load it into an internal register, do the operation there, and write it back to memory if it's the destination operand; but from the point of view of the compiler, the CPU is operating directly on memory. > (or are some operations possible on memory without going to registers?) Some atomic memory operations (like atomic compare and exchange) can be thought of as being done directly on memory (or on the cache which sits above the memory). Some CPUs might even implement it that way (by having an "atomic memory operation" command between the CPU and the cache, instead of doing the operation on the CPU).