Summary: On the In uence of Lookahead in Competitive
We introduce a new model of lookahead for on-line paging algorithms and study several
algorithms using this model. A paging algorithm is on-line with strong lookahead l if it sees
the present request and a sequence of future requests that contains l pairwise distinct pages.
We show that strong lookahead has practical as well as theoretical importance and improves
the competitive factors of on-line paging algorithms. This is the rst model of lookahead
having such properties. In addition to lower bounds we present a number of deterministic
and randomized on-line paging algorithmswith strong lookahead which are optimalor nearly
Keywords: On-Line Algorithms, Paging, Lookahead, Competitive Analysis.
In recent years, the competitive analysis of on-line algorithms has received much attention.
Among on-line problems, the paging problem is of fundamental interest. Consider a two-level
memory system which has a fast memory that can store k pages and a slow memory that can
manage, basically, an unbounded number of pages. A sequence of requests to pages in the
memory system must be served by a paging algorithm. A request is served if the corresponding
page is in fast memory. If the requested page is not stored in fast memory, a page fault occurs.