This course is an introductory course on computer systems. It introduces computer systems from a programmer's perspective, rather than a system implementer's perspective, which prepares students for more advanced topics that discuss the internals of a computer system (e.g., operating systems or computer architecture). As a result, the focus of the course is teaching programmable interfaces of a computer system as well as how to use them correctly and effectively when writing a program. The topics mainly include hardware/software interfaces (e.g., data representation in memory) and OS/application interfaces (e.g., syscalls). In discussing these topics, the course gives an overview of a complete computer system, the hardware, operating system, compiler, and network, in order to guide students through various components that modern programs rely on to accomplish their intended purposes.