PLRU example 2

Same as before, except:
check_frames = 2

num_frames = 6, page_size = 512
lookahead = 3, check_frames = 2
Current operation:
w 1492	(page 2)
Lookahead list:
w 50	(page 0)
w 15400	(page 30)
r 2200	(page 4)