This introductory text offers a contemporary treatment of computer architecture using assembly and machine language with a focus on software. Students learn how computers work through a clear, generic presentation of a computer architecture, a departure from the traditional focus on a specific architecture. A computer's capabilities are introduced within the context of software, reinforcing the software focus of the text. Designed for computer science majors in an assembly language course, this text uses a top-down approach to the material that enables students to begin programming immediately and to understand the assembly language, the interface between hardware and software. The text includes examples from the MIPS RISC (reduced instruction set computer) architecture, and an accompanying software simulator package simulates a MIPS RISC processor (the software does not require a MIPS processor to run).