The primary object of this manual is to build an understanding of the principles of computer operations and the use of computers in the laboratory. While the development of applications for computers has been rapid since their introduction, the principles of computer operation and their use in sensing and control have remained stable. Those are the primary subjects of this book, throughout which a gradual understanding of what goes on inside a computer is developed. The laboratory provides a vital experience in linking theory with physical reality, and all of the computer work is done in the context of doing experiments. The IBM-PC design is used as the basis for the book. The internal design of this machine is slightly more complicated than earlier personal computers, but it is still simple enough to be quickly learned. The computer can be directly controlled by proper programming, and offers considerably more power than earlier designs. The IBM design also has expansion slots which make the addition of special hardware capabilities relatively simple, and provide a great flexibility in interfacing the machine to other equipment. The book, based on courses given at Cornell University, is designed as a tutorial to be used in conjunction with laboratory work. It will be a valuable guide and reference for students who are familiar with first-year university physics and have some computing experience.