Question

Consider the following two page replacement strategies: FIFO (First-In, First-Out) is a page replacement strategy in which the page that is evicted is the one that has been currently in the cache for the longest duration. LIFO (Last-in, First-Out) is a page replacement strategy in which the page that is evicted is the one that was brought into cache most recently in time. (a) (4 pts) Show that neither FIFO nor LIFO is a marking algorithm. The following definition applies to parts (b) and (c)

Answer 1

FIFO and LIFO are not marking algorithms because they do not differentiate between active and inactive pages when deciding which one to evict. FIFO evicts the oldest page, and LIFO evicts the most recent page, without regard for current usage, violating the principle of marking algorithms.

Step-by-step explanation:

To demonstrate that neither First-In, First-Out (FIFO) nor Last-In, First-Out (LIFO) is a marking algorithm, we must refer to the definition of a marking algorithm. A marking algorithm guarantees that no page in a set of pages that is in active use (or 'marked') will be evicted before any page that is not in active use (or 'unmarked').

In the case of FIFO and LIFO, neither strategy makes any distinction between active and inactive pages. FIFO evicts the page that has been in cache the longest, regardless of whether it is currently in use. On the other hand, LIFO evicts the most recently added page, again without any regard to whether it is in active use. Therefore, it is possible for both FIFO and LIFO to evict pages that are in active use before considering those that are not, which indicates that they do not adhere to the marking principle.

For example, consider a cache where a page that was added first is still in active use. Under FIFO, this page could be evicted simply because of its arrival time, not based on its current usage status. Similarly, if a newly added page is immediately in active use, LIFO could evict it purely because it is the latest addition.