Text Files

A computer application (program) is the context for the bit patterns of its input and output files. Although there are some standard contexts (such as for text files), many applications use a context that is their own. If you could somehow inspect the surface of a disk and see the bit patterns stored in a particular file, you would not know what they represented without additional knowledge.

Often people talk of "text files" and "MS Word files" and "executable files" as if these were completely different things. But these are just sloppy, shorthand phrases. For example, when someone says "text file" they really mean:

Text File: A file containing a sequence of bytes. Each byte holds a bit pattern which represents a printable character or one of several control characters (using the ASCII encoding scheme). Not all control characters are allowed. The file can be used with a text editor and can be sent to a hardware device that expects ASCII character codes.

Files containing bytes that encode printable characters according to the ASCII convention have about half of the possible patterns. Computer monitors and printers behave correctly with the ASCII patterns, but often can't deal with the other patterns.