Computer Systems covers topics you need to know to become a better programmer. Author Martin Kalin draws on knowledge he gained writing large industrial applications, web and non-web alike: for those applications, it's always the systems issues that come to the fore—running short on or out of memory, application crashes and restarts, running too slowly, contending with problems on the host machine, and so on.

The emphasis in the book, from start to finish, is on how an understanding of the underlying computer system is essential to writing correct, robust, and efficient code—regardless of the language or the run-time context (e.g., JavaScript executing in a browser context, an Objective C app running on an iPad, a Rails web site hosted on Heroku, etc.). It answers questions such as:
* When my program runs, what resources does it need? (CPUs, memory, I/O devices, etc.)
* How does my program get these resources? (Calls to operating system routines, implicitly or explicitly made.)
* How does the way in which I write code--the way I structure my program--impact the efficiency of resource use?