Offering a simplified approach to the understanding of computer science, this fourth edition contains changes in content and layout which are aimed not just at covering the material on the latest syllabuses, but at helping the reader's study for the latest examinations. Parts targeted at contemporary computer applications and applications packages have been introduced, reflecting a significant shift in emphasis in examinations over recent years. Graphical user interfaces (GUIs), development methodologies, desktop computers, applications packages and databases have been given more emphasis to reflect the examination requirements of developing and using computer systems, and obsolete material has been removed. A free Lecturers' Supplement is provided. An ELBS/LPBB edition is available.