Exam Prep — Midterm

This page summarises everything to review before the midterm and provides practice questions drawn from the lecture notes. See Course Overview for the full topic index. [OS Course Notes — Weeks 3 & 5.md]

[OS Course Notes — Weeks 3 & 5.md]

Processes

• Define a process and explain how it differs from a program (active vs. passive entity). → Processes
• List and describe all five process states: new → ready → running → waiting → terminated.
• Explain what a PCB (Process Control Block) stores (state, PC, registers, memory info, open files).
• Describe the context switch: what is saved/restored, and why it is pure overhead.

Threads

• Define a thread as a unit of execution within a process. → Threads
• State what threads share (code, data, heap) vs. what is private (stack, registers).
• List the four benefits of multithreading: responsiveness, resource sharing, economy, multicore utilisation.
• Identify the key downside: race conditions when sharing resources.

CPU Scheduling

• State the scheduling goals: maximise CPU utilisation & throughput; minimise waiting, response, and turnaround time. → CPU Scheduling
• Know each algorithm's behaviour, strengths, and weaknesses:

• Distinguish preemptive (CPU can be reclaimed mid-burst) from non-preemptive (process holds CPU until it yields).
• Practice average waiting time calculations using hand-drawn Gantt charts for each algorithm.

1. 1.Process vs. Program — A .exe file sitting on disk vs. that same file loaded and running: which is a process, and what additional data structures does the OS create for it? [OS Course Notes — Weeks 3 & 5.md]

1. 2.State Transitions — Draw the five-state process diagram. What event causes a transition from *running* → *waiting*? What brings a process back to *ready*? [OS Course Notes — Weeks 3 & 5.md]

1. 3.Context Switch Cost — Why is a context switch described as "pure overhead"? Under what scheduling conditions does excessive switching hurt throughput? [OS Course Notes — Weeks 3 & 5.md]

1. 4.Threads Sharing — Two threads in the same process both increment a shared counter. Why can this produce incorrect results, and what is the term for this problem? [OS Course Notes — Weeks 3 & 5.md]

1. 5.Gantt Chart Calculation — Given three processes arriving at time 0 with CPU bursts of 8, 2, and 4 ms, calculate the average waiting time under (a) FCFS, (b) SJF, and (c) Round Robin with quantum = 3 ms. [OS Course Notes — Weeks 3 & 5.md]

1. 6.Starvation & Aging — Which two scheduling algorithms risk starvation? How does *aging* solve the problem in Priority Scheduling? [OS Course Notes — Weeks 3 & 5.md]

1. 7.Preemptive vs. Non-preemptive — Give one example of each type from the algorithms covered. In a preemptive system, what triggers the CPU to be reclaimed? [OS Course Notes — Weeks 3 & 5.md]

See the full Key Concepts Glossary for one-line definitions of every core term.

[OS Course Notes — Weeks 3 & 5.md]