The document summarizes the evolution of operating systems from early batch systems to modern distributed systems. It describes batch operating systems which executed jobs sequentially in batches. Multiprogramming systems allowed the CPU to run multiple processes by switching between them when one was waiting for I/O. Time-sharing systems further improved resource sharing by rapidly switching between user programs. Real-time systems guarantee response times for critical applications. Network and distributed systems connect multiple computers and allow resources to be shared across a network or distributed architecture.