Solution

Concept:

Elevator algorithm (also SCAN) is a disk-scheduling algorithm to determine the motion of the disk's arm and head in servicing read and write requests.This algorithm is named after the behavior of a building elevator, where the elevator continues to travel in its current direction (up or down) until empty, stopping only to let individuals off or to pick up new individuals heading in the same direction.

A Process Scheduler schedules different processes to be assigned to the CPU based on particular scheduling algorithms. These algorithms are either non-preemptive or preemptive. Non-preemptive algorithms are designed so that once a process enters the running state, it cannot be preempted until it completes its allotted time, whereas preemptive scheduling is based on priority where a scheduler may preempt a low-priority running process anytime when a high-priority process enters into a ready state.

A stack-based algorithm is one for which it can be shown that the set of pages in memory for N frames is always a subset of the set of pages that would be in memory with N+1 frames. For LRU replacement, the set of pages in memory would be the n most recently referenced pages. If the number of frames increases then these n pages will still be the most recently referenced and so, will still be in the memory. While in FIFO, if a page named b came into physical memory before a page a then priority of replacement of b is greater than that of a, but this is not independent of the number of page frames and hence, FIFO does not follow a stack page replacement policy and therefore suffers Belady’s Anomaly. 

Havender’s Algorithm is the Elimination of “Mutual Exclusion” Condition The mutual exclusion condition must hold for non-shareable resources. That is, several processes cannot simultaneously share a single resource. This condition is difficult to eliminate because some resources, such as the tap drive and printer, are inherently non-shareable. Note that shareable resources like read-only-file do not require mutually exclusive access and thus cannot be involved in deadlock. Elimination of “Hold and Wait” Condition There are two possibilities for the elimination of the second condition. The first alternative is that a process request be granted all the resources it needs at once, prior to execution. The second alternative is to disallow a process from requesting resources whenever it has previously allocated resources. This strategy requires that all the resources a process will need must be requested at once. The system must grant resources on “all or none” basis. If the complete set of resources needed by a process is not currently available, then the process must wait until the complete set is available. While the process waits, however, it may not hold any resources. Thus the “wait for” condition is denied and deadlocks simply cannot occur.

The Correct Answer is option 1.