The primary aim of the present paper is to modify the performance model of Boseand Cheng [1] to a more realistic case when external visits are also allowed to the remote Web servers and the Web servers have limited buffer. We analyze how many parameters affect theperformance of a Proxy Cache Server. Numerical results are obtained for the overall response time with and without a PCS. These results show that the benefit of a PCS depends on variousfactors. Several numerical examples illustrate the effect of visit rates, visit rates for the external users , and the cache hit rate probability on the mean response times.