In Lecture 5, we leap into the "Limited Direct Execution" protocol, a pivotal technique designed by operating system (OS) developers to optimize program execution speeds. The core principle of limited direct execution involves allowing programs to run directly on the CPU to maximize efficiency. However, this straightforward approach introduces several challenges, notably in ensuring restricted operations and managing context switching. The lecture discusses how the OS maintains control and security through mechanisms like user and kernel modes, which restrict the operations a program can perform directly, and system calls, which provide a controlled gateway for executing privileged operations. Further, it explores the intricacies of handling system calls, including the transition between user and kernel modes, saving and restoring process states, and managing system call numbers to invoke specific OS services securely. Additionally, the lecture covers the protocol for switching between processes, addressing cooperative and non-cooperative approaches, and the vital role of the scheduler. It concludes by examining the handling of interrupts, particularly during system calls, and the strategies employed to maintain system integrity and prevent concurrent access issues. This comprehensive overview equips students with a deeper understanding of how OSes manage to run programs efficiently while maintaining a secure and controlled environment.
This is a follow-up video from Lecture 3 Process Abstraction going into a bit more detail to help you understand not only the process abstraction and multi-programming, but the mechanism involved in enabling the virtualization of the CPU.
https://youtu.be/DKmBRl8j3Ak?si=h9S18hc71Gt_Srzo
FA 2024 slides:
https://docs.google.com/presentation/d/1zBpYsvNIwMW8OmPF1hp-TTTGMhWDHrIG88OwU-ZaaFk/edit?usp=sharing
Original slides:
https://docs.google.com/presentation/d/1y3RvHap6EvsV_1OkaIF9XGROOJHQrLRU5UiwalSTb2I/edit?usp=sharing
No example code for this lecture.
No additional references or resources at this time.