Traps and Interrupts: Mechanisms for Operating System Control

This lecture covers the concepts of traps, interrupts, and exceptions within computer systems. It begins by defining traps and exceptions, explaining their roles in handling internal program errors such as division by zero and illegal memory access. The instructor discusses how the operating system (OS) configures hardware at boot time to manage these events through a trap table, which specifies the appropriate handlers for various exceptions. The lecture highlights the challenges of limited direct execution, particularly in ensuring that processes do not execute privileged code and that the OS maintains control over CPU execution. It contrasts cooperative and non-cooperative approaches to process management, emphasizing the importance of interrupts as asynchronous signals that allow the OS to regain control. The handling of interrupts is detailed, including the transition from user mode to kernel mode and the execution of interrupt handling code. The lecture concludes with a summary of the hardware support necessary for modern operating systems, focusing on protection mechanisms and the implementation of system calls.