The objective of this book is to make it possible (and even easy) for students to master both assembly language and the fundamentals of computer architecture in a single semester. Integrating coverage of software and hardware throughout, the book uses H1--a simple, horizontally microprogrammed computer--as a unifying theme. Like all simple models, H1 has flaws, but this book puts these flaws to good use. In particular, in addition to showing students how H1 works and what is wrong with it, the book shows students how to fix it (which they then proceed to do). Students learn best by doing, and this book supplies much to do with various examples and projects to facilitate learning. For example, students not only use assemblers and linkers, they also write their own. Students not only study and use the provided instruction set but implement new, improved ones. The result is a book that is easy to read, engaging, and substantial. The software package for the book supports Windows, Mac OS X, Linux, and Raspbian.