Computers are no longer just for specialists. Today, computing is not just a profession and a hobby; it is also a tool used in virtually all human activities. That’s why we’ve compiled this book of background knowledge. Its purpose is to tell you the things other people think you already know. We design this book to have a convenient size so it can be easily carried around. In compiling a book this size, we have had to be selective. The quickest way to identify a word that you can’t find in a book is probably to do a web search. Also, some terms are almost always abbreviated, and in that case you should look for the abbreviation rather than the full term.