Martin Thompson, proprietor of the blog Mechanical Sympathy, founder of the LMAX disruptor open source project, and a consultant and frequent speaker on high performance computing talks with Robert about computer program performance. Martin explains the meaning of the term “mechanical sympathy,” derived from auto racing, and its relevance to program performance: the importance of code that takes into account the computer architecture. The discussion proceeds to cover the basics of hardware architecture, and then Martin continues with a discussion of the costs of different program characteristics in a multi-core processor. Two key quantitative constraints, Amdahl’s Law and Little’s Law, are covered next. The discussion evolves into issues facing application programmers, such as poorly implemented libraries and frameworks, lock-free algorithms, and the impact of java garbage collection. The conversation wraps up with some thoughts on the proper methodology for approaching program performance.