Processes & Threads

Address spaces, the PCB,<br>context switches & threads

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How the OS turns a program into a process, what the PCB tracks, how threads share memory within a process, and why that sharing is both powerful and dangerous.

By the end, you can

Explain the difference between a program (file on disk) and a process (running instance with address space and PCB).
Name the four segments of a process address space and state the purpose of each.
List the six fields of a PCB and explain why each is needed.
Trace a process through all five states and name the transitions between them.
Describe the steps of a context switch and explain why it is pure overhead.
Explain what fork() and exec() each do and how they combine to launch a new program.
State what threads share and what is private per thread, and correct the misconception that threads have separate heaps.
Explain why same-process thread switching is cheaper than process switching (TLB flush, cache warmth).
Distinguish user-level from kernel-level threads and explain the blocking hazard of user-level threads.
Compare the isolation-vs-sharing trade-off of processes versus threads, and name three IPC mechanisms.

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