In addition to extending production operating systems, researchers have implemented specialized or new operating systems to experiment with Web server performance. The Lava hit-server [19] achieves cache performance limited only by memory bus bandwidth. While this paper holds the TCP/IP stack, network driver, and network hardware fixed, the hit-server focuses on network driver optimizations and a non-TCP transport protocol to minimize memory conflicts between the CPU and network controller for performance. The Cheetah Web server [20] is another example of a Web server designed with performance in mind on a new operating system. Rather than extending production systems as described in this paper, the Cheetah Web server uses a specialized TCP stack on a research operating system called Exokernel [21]. The Exokernel approach demonstrates the performance possible when subsystems such as the network stack and file system are tightly integrated. The AFPA results in this paper appear consistent with the factor of three to six performance gain reported for Cheetah on the Exokernel operating system. However, the AFPA results use unmodified, production operating systems allowing direct comparisons with state of the art user-mode optimizations on Linux and Windows 2000.