  Replicating or caching popular content in memories distributed across the
network is a technique to reduce peak network loads. Conventionally, the
performance gain of caching was thought to result from making part of the
requested data available closer to end users. Recently, it has been shown that
by using a carefully designed technique to store the contents in the cache and
coding across data streams a much more significant gain can be achieved in
reducing the network load. Inner and outer bounds on the network load v/s cache
memory tradeoff were obtained in (Maddah-Ali and Niesen, 2012). We give an
improved outer bound on the network load v/s cache memory tradeoff. We address
the question of to what extent caching is effective in reducing the server load
when the number of files becomes large as compared to the number of users. We
show that the effectiveness of caching become small when the number of files
becomes comparable to the square of the number of users.
