Which is more efficient, basic mutex lock or atomic integer?

Question

For something simple like a counter if multiple threads will be increasing the number. I read that mutex locks can decrease efficiency since the threads have to wait. So, to

Answer 1

atomic integer is a user mode object there for it's much more efficient than a mutex which runs in kernel mode. The scope of atomic integer is a single application while the scope of the mutex is for all running software on the machine.