File Overhead and Other Features

When data you create is stored in a computer, it must be stored in a particular arrangement suitable for the program that created the information. This arrangement of information is called the file format .

A few programs, such as MS-DOS Edit and Windows Notepad, store only the text you create. What if you want to boldface a certain word in the text? A text-only editor can't do it. All that Edit and Notepad can store is text. As you have seen, in text-only storage, a character equals a byte.

In computer storage, however, pure text is seldom stored alone. WordPad and other word-processing programs such as Microsoft Word and Corel WordPerfect enable you to boldface , underline , italicize , and make text larger or smaller. You can also use different fonts in the same document (see Chapter 10, "Printers," for more about that).

Most modern programs also enable you to insert tables, create columns of text, and insert pictures into the text. Some, such as Microsoft Word, have provisions for tracking changes made by different users. In other words, there's a whole lot more than text in a document.

To keep all this non-text information arranged correctly with the text, WordPad and other programs must store references to these additional features along with the text, making even a sentence or two into a relatively large file, even if none of the extra features is actually used in that particular file. Thus, for most programs, the bytes used by the data they create is the total of the bytes used by the text or other information created by the program and the additional bytes needed to store the file in a particular file format.

Because different programs store data in different ways, it's possible to have an apparent software failure take place because a user tries to open a file made with program A with program B. Unless program B contains a converter that can understand and translate how program A stores data, program B can't read the file, and might even crash. To help avoid problems, Windows associates particular types of data files with matching programs, enabling you to open the file with the correct program by double-clicking the file in Explorer or File Manager. You'll learn more about file associations in Chapter 18, "Using and Optimizing Windows."