Darwin offers several tools for measuring the CPU usage. These are especially convenient when attempting to optimize your code and make projections about the necessary time required to complete a long computation. Programs written in Darwin code can sometime run much slower than written in another language such as C. Unfortunately, writing programs in C can be a non-trivial exercise. This trade-off leads to questions about when Darwin code will suffice for the task at hand and when another language must be used. Measuring the performance of your Darwin prototypes is a necessary step towards resolving this issue. Chapter contains a working example of how to go about this. This section explores some of the primitive functions Darwin offers.