Recognize interaction and synchronization among process

• Many systems provide hardware support for critical section code
• Uniprocessors – could disable interrupts
• Currently running code would execute without Preemption.
• Generally too inefficient on multiprocessor systems
• Operating systems using this not broadly scalable
• Modern machines provide special atomic hardware instructions
• Atomic = non-interruptable
• Either test memory word and set value or swap contents of two memory words