This Encyclopaedia is an Introductory Computer Science which will serve well for mature students who need a command of this important field. Undergraduate students will find the presentation logical, the examples thoughtful, and the coverage thorough. Students and professionals for whom memory or mastery of previous computer courses have dimmed, will find, in addition to the above virtues. This Encyclopaedia is an introduction to the principles of computer science, linking its scientific aspects with practical applications. It is addressed to both readers who wish to learn hardware and software and those seeking to understand computer devices. It is particularly well suited for those who want to do both.