clock replacement algorithm

Test Your Knowledge

Quiz: The Clock Replacement Algorithm

Instructions: Choose the best answer for each question.

1. What is the primary purpose of the Clock Replacement Algorithm?

a) To manage the clock time in a system. b) To determine which page in memory to evict when a new page needs to be loaded. c) To store and retrieve data from secondary storage. d) To allocate memory to different processes.

2. What does the "use bit" represent in the Clock Algorithm?

a) The time a page was last accessed. b) The size of a page. c) The priority of a page. d) Whether a page has been recently used.

3. How does the Clock Algorithm handle page replacement?

a) It always replaces the oldest page in memory. b) It replaces the page with the smallest use bit value. c) It replaces the page with the use bit set to 0 after a complete cycle of the pointer. d) It replaces the page with the highest priority.

4. Which of the following is an advantage of the Clock Algorithm?

a) It always guarantees the fastest page replacement. b) It is very complex to implement. c) It provides a balance between recency and age considerations. d) It requires a large amount of memory overhead.

5. What is another name for the Clock Replacement Algorithm?

a) Least Recently Used (LRU) Algorithm b) First-In-First-Out (FIFO) Algorithm c) First-In-Not-Used-First-Out (FINUFO) Algorithm d) Second Chance Algorithm

Exercise: Simulating the Clock Algorithm

Instructions:

Consider a system with a memory capacity of 4 pages. Use the following page access sequence to simulate the Clock Algorithm:

Page Access Sequence: 1, 2, 3, 4, 1, 2, 5, 1, 2, 3

Task:

1. Initialize: Start with an empty memory.
2. Load: Load the first 4 pages (1, 2, 3, 4) into memory. Set their use bits to 0.
3. Simulate: For each subsequent page access, follow the Clock Algorithm steps:
   • Update the use bit of the accessed page.
   • Advance the pointer.
   • Check the use bit of the current page. If it's 0, replace that page with the new access.
4. Record: Note the replaced page for each access.

Example:

For the first access (1), the pointer will move to the entry for page 1, set the use bit to 1, and advance. The pointer will then be at page 2, with a use bit of 0. Since page 2 has not been used recently, it will be replaced by page 1.

Complete the simulation and record the replaced pages for each access in a table.

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