A system has four frames. The time of loading, time of last access, and the R(reference) and M (modified) bits for each page are as shown below. The times are in clock ticks:

page	loaded	last ref.	R	M
0	126	280	1	0
1	230	265	0	1
2	140	270	0	0
3	110	285	1	1

For each of the following page replacement algorithms, determine which page will be replaced:

1. Second Chance
2. LRU
3. CLOCK

b) Consider a file whose size varies between 4Kb and 4MB during its lifetime. State, with a reason, whether or not the following allocation schemes will be appropriate for implementing the file storage: contiguous allocation, linked list allocation, file allocation table

c) In the case of an external USB hard drive attached to a computer, which is more suitable a write-through cache or nonwrite-through cache.

d) Write down the average access time for a disk cache given that the h% of the time it takes 1ms to satisfy a request from the cache and that 75ms is needed to satisfy a request if a disk read is necessary.

e) (i)Describe how to implement a lock using semaphores.

(ii)What is a test-and-set instruction? How can it be used to implement mutual exclusion? You may include a segment of pseudo-assembly code to aid your explanation.