CS CS Operating Systems & Memory Management 1 — Questions and Answers
Question 1: What is a deadlock in operating systems?
- A process that consumes 100% CPU without terminating
- A situation where two or more processes wait indefinitely for resources held by each other (Correct answer)
- A memory allocation error causing a page fault
- A kernel panic caused by a device driver
Correct answer: A situation where two or more processes wait indefinitely for resources held by each other
Deadlock occurs when a set of processes are each waiting for a resource held by another process in the set, so none can proceed.
Question 2: Which page replacement algorithm replaces the page that will not be used for the longest time in the future?
- FIFO (First-In, First-Out)
- LRU (Least Recently Used)
- OPT (Optimal) (Correct answer)
- Clock Algorithm
Correct answer: OPT (Optimal)
The Optimal (OPT) algorithm is theoretically perfect but impractical because it requires future knowledge of which pages will be accessed next.
Question 3: What is the difference between a process and a thread?
- A thread has its own memory space while a process shares memory with others
- A process is an independent execution unit with its own memory space, while threads share memory within a process (Correct answer)
- Threads cannot run in parallel on multi-core CPUs
- Processes are lighter weight than threads
Correct answer: A process is an independent execution unit with its own memory space, while threads share memory within a process
A process has its own isolated memory space, while threads within the same process share the same heap and data segments, making inter-thread communication faster but requiring synchronization.
Question 4: What does a context switch entail in an operating system?
- Switching the CPU from user mode to kernel mode
- Saving the state of a running process and restoring the state of another so the CPU can switch tasks (Correct answer)
- Allocating a new memory page for a process
- Flushing the disk write cache to storage
Correct answer: Saving the state of a running process and restoring the state of another so the CPU can switch tasks
A context switch saves the CPU registers and process state of the current process to its PCB and loads the saved state of the next scheduled process.
Question 5: In virtual memory, what is a 'page fault'?
- A hardware error in the physical RAM chips
- An interrupt triggered when a process accesses a page not currently loaded in physical memory (Correct answer)
- A bug in a process that causes an illegal memory write
- An overflow of the page table beyond available address space
Correct answer: An interrupt triggered when a process accesses a page not currently loaded in physical memory
A page fault occurs when a process references a virtual memory page that is not currently mapped to a physical frame, causing the OS to load it from disk.
Question 6: Which CPU scheduling algorithm provides the best average waiting time for a given set of processes?
- Round Robin
- First-Come First-Served (FCFS)
- Shortest Job First (SJF) (Correct answer)
- Priority Scheduling
Correct answer: Shortest Job First (SJF)
SJF minimizes average waiting time by always executing the process with the shortest expected CPU burst next, which is optimal for batch workloads.
CS CS Operating Systems & Memory Management 1
What is a deadlock in operating systems?