Most programs read most of their data from disk files, and write most of their results to other disk files. For example, when you create a document with a word processor (such as Microsoft Word) you save your work in a disk file (called something like mywork.doc). Later on, you can retrieve that data and continue working on it, or do other things to it, such as print it or e-mail it.
This chapter discusses how to write programs that save data to disk files.
Say that you have just recieved your monthly credit card bill. Where was all the data in that bill kept during the past month?