Part 4 begins by giving examples of representing computer systems as networks of queues that may be evaluated analytically. Jackson networks, BCMP queues and Gelenbe networks are presented as exact analytical solutions techniques that can be used to evaluate system performance in a variety of applications. A detailed example of a computer system with virtual memory is given and its solution as a closed Jackson network is presented. The non-analytical approach of discreet event simulation (DES) is subsequently covered along with the important issues of DES time management, event generation and synchronization, and DES statistical validation. Part 4 is concluded with a coverage of approximate solutions techniques. The approach of diffusion approximations is introduced and is applied to general networks of queues with one customer class. The approach is then used to solve a practical application involving packet switching networks. Finally the approach of fixed-point iterations is covered and is used to solve a practical application involving a distributed shared memory system.