This paper presents an execution-driven simulator called Trojan, which is an extended version of MIT Proteus, for evaluating the performance of parallel shared-memory machines. The key features of Trojan are: 1) it simulates efficiently both process-model based (e.g., SPLASH) and thread-model based applications (e.g., SPLASH2) (a "copy-on-write'' mechanism is used on process-based applications implemented on a threads package); 2) it provides support for virtual memory simulation, which is, to our knowledge, the first execution-driven simulator to offer this functionality; and 3) Trojan does not require making any modification to applications, which results in increased accuracy and usability. We have used Trojan extensively to study cache behavior, network traffic patterns, multiprocessor architectures, and application behavior.