Why is the volatile keyword important in embedded C programming?

The volatile keyword tells the compiler that a variable's value may change unexpectedly (outside normal program flow), preventing optimizations that could cause incorrect behavior. Essential uses: Hardware registers (may change between reads), Variables modified by ISR (main code must see updates), Variables used by multiple threads, and Memory-mapped I/O. Without volatile, compiler may: cache register values, reorder or eliminate reads/writes, or optimize away seemingly redundant operations. Proper use prevents hard-to-debug timing and synchronization bugs in embedded systems.