Page replacement algorithms (FIFO, LRU, Optimal) in Operating Systems - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the FIFO page replacement algorithm?

FIFO (First-In, First-Out) replaces the oldest page in memory first. It removes pages in the order they were loaded, like a queue.

beginner

How does the LRU page replacement algorithm decide which page to remove?

LRU (Least Recently Used) removes the page that has not been used for the longest time. It assumes pages used recently will be used again soon.

intermediate

What is the Optimal page replacement algorithm?

The Optimal algorithm replaces the page that will not be used for the longest time in the future. It gives the best performance but needs future knowledge.

beginner

Which page replacement algorithm is easiest to implement but may cause more page faults?

FIFO is the easiest to implement because it only tracks the order pages arrived. However, it can cause more page faults because it ignores usage patterns.

intermediate

Why is the Optimal page replacement algorithm not used in real systems?

Because it requires knowing the future sequence of page requests, which is impossible in real time. It is mainly used as a benchmark.

Which page replacement algorithm removes the oldest page in memory first?

A Optimal

B FIFO

C LRU

D Random

FIFO removes pages in the order they were loaded, so the oldest page is replaced first.

LRU stands for:

A Least Frequently Used

B Last Recently Used

C Least Recently Used

D Longest Running User

LRU means Least Recently Used, which replaces the page not used for the longest time.

Which algorithm requires knowledge of future page requests?

A Optimal

B LRU

C Clock

D FIFO

The Optimal algorithm replaces the page that will not be used for the longest time in the future, needing future knowledge.

Which algorithm is easiest to implement?

A Optimal

B Second Chance

C LRU

D FIFO

FIFO is simple because it only tracks the order pages arrived, no complex tracking needed.

Why might FIFO cause more page faults than LRU?

A Because it ignores how often pages are used

B Because it removes the most recently used page

C Because it predicts future page use

D Because it uses a random selection

FIFO ignores usage patterns and removes pages just based on arrival order, which can cause more faults.

Explain how FIFO, LRU, and Optimal page replacement algorithms decide which page to remove.

Think about the order of page usage and future knowledge.

Discuss the advantages and disadvantages of FIFO and LRU algorithms.

Consider ease of implementation and fault rates.