An operating system manages computer hardware resources and provides common services for programs. It performs key functions like process management, memory management, I/O device management, and a user interface. Operating systems have evolved from vacuum tube-based serial processing systems to today's personal computing systems. They have progressed from simple batch OSes to multi-programming OSes to time-sharing OSes. In conclusion, operating systems allocate resources, support applications and utilities, and control hardware while providing a user interface.