Garbage collection yields numerous software engineering benefits, but its quantitative impact on performance remains elusive. One can compare the cost of conservative garbage collection to explicit memory management in C/C++ programs by linking in an appropriate collector. This kind of direct comparison is not possible for languages designed for garbage collection (e.g., Java), because programs in these languages naturally do not contain calls to free. Thus, the actual gap between the time and space performance of explicit memory management and precise, copying garbage collection remains unknown. We introduce a novel experimental methodology that lets us quantify the performance of precise garbage collection versus explicit memory management. Our system allows us to treat unaltered Java programs as if they used explicit memory management by relying

Computer Science To Sarah for reminding me of everything I can do and to Shoshanna for inspiring me to do more. ACKNOWLEDGMENTS I am most grateful to my advisor, Emery Berger, for everything he has done throughout this thesis. I appreciate his guidance, suggestions, and inspiration. I feel especially fortu-nate for the patience he has shown with me throughout all the twists and turns my life took getting through this dissertation. I must also thank Eliot Moss and Kathryn McKinley for their leadership and support. I will be forever grateful that they took a chance on a student with a less-than-stellar aca-demic record and provided me with a fertile, inspiring research environment. They are both very knowledgeable and I benefited from our discussions in a myriad of ways. They have also served as members of my committee and I appreciate their helpful comments and sug-gestions. Thanks also to Scott Kaplan, another member of my committee, for his advice and feedback.