17.2.6 Worked Examples: Operating Systems

TL;DR

Understanding how an operating system manages processes and shared address space on a computer.

Transcript

In order for multiple processes to be able to run on the same computer, using a shared address space, we need to have an operating system that controls which process gets to run at any given point in time and ensures that the state that is currently loaded into the system is the state of the current process. Through the following example we will ta... Read More

Key Insights

• ❓ Operating systems are necessary for managing multiple processes and ensuring the correct state is maintained for each process.
• 👣 MState and ProcTbl are data structures used by operating systems to track register values and process state.
• 🏪 The Scheduler is responsible for process switching, storing and loading states accordingly.
• 🔄 The SamplePC supervisor call retrieves the program counter value for a particular process.

Questions & Answers

Q: How does the operating system manage multiple processes on a computer?

The operating system utilizes MState to track register values and a process table (ProcTbl) to store state for each process. The Scheduler is responsible for switching between processes, storing and loading their states accordingly.

Q: What additional state can be stored per process in the process table?

In addition to register values, the process table can store other state, such as a page map for virtual memory usage or a keyboard identifier to associate hardware with a specific process.

Q: How does the SamplePC supervisor call work?

The SamplePC supervisor call takes a process number as input and returns the value of the program counter (PC) for that process. It reads the XP register from ProcTbl to determine the next PC value for the process.

Q: How can repeated samples be avoided when using the SamplePC call?

To avoid repeated samples, a call to the Scheduler can be added in the SamplePC handler. This ensures that the profiler process only samples a single PC value before allowing another process to run.

Summary & Key Takeaways

• Operating systems control the running of multiple processes on a computer, ensuring that the current state is maintained and managing process scheduling.

• The operating system uses a structure called MState to track register values for running processes, and a process table (ProcTbl) to store necessary state for each process.

• The Scheduler is responsible for switching control from one process to another, storing the state of the currently running process and loading the state for the new process.