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Running MS DOS, by Van Wolverton, pages 26-27
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When you test drive a car, you already know how to start it.  The
test drive is to help you become familiar with the controls, the
steering, the brakes, the overall "feel" of the car.  Now it's
time to take a test drive with DOS.  Your learned how to start
DOS in the last chapter.  It's time to begin learning how to
control DOS, how to "steer" it in the direction of one task of
another, and how to call a halt when you want or need to.

That's what this chapter is all about.  It introduces you to the
directory of files that DOS keeps on each disk, and shows you how
to use the specific keys on your keyboard.   You use these keys
to tell DOS to cancel lines or commands, freeze the display, and
restart DOS.

To try the examples given here, start up your computer, as you
did in the last chapter.  Enter the appropriate date and time, so
that DOS responds with the system prompt, A> (C> of you are using
a fixed disk).  Don't worry about leaving your computer on while
you read the text between examples; DOS is patient.

Note:  Part of this chapter deals with keys that have special
meaning for DOS.  If you are not using an IBM personal computer,
you may want to check your documentation for equivalent keys on
your system.

Recall from Chapter 1 that information stored on a disk is stored
as a file.  DOS automatically keeps and updates a list of every
file you save on every diskette you use.  This list is called
directory.  If you create and save a new file, DOS adds it to the
list.  If you revise and old file, DOS keeps track of that, too. 
The directory eliminates the need to keep a separate record of
everything you save on each diskette.  You can tell DOS you want
to see the directory whenever DOS is displaying the system
prompt.

The example on the next section serves the double purpose of
showing you a directory and showing you around the DOS system
disk itself.  As you use the system more, you will come to
recognize many of the DOS commands.  Before you look at a
directory, though, you should know a little about how DOS saves
your files.

Whenever you create a file, you give it a name, called the file
name, of up to eight characters.  Of you wish, you can add a
suffix, called the extension, of up to three more letters. 
(Chapter 4 and 5 present more on files).  
Whenever you ask DOS to show you the directory of a diskette, it
lists your files by name (and extension, if there is one).  It
also shows you the size of your file, in units called bytes, and
it gives you the date and the time file was either created or
last changed (that's why DOS prompts you for the date and time).

Note:  A byte is the amount of storage required to hold one
character in computer memory or on a disk.  Here are a few
familiar items and their sizes, in bytes: the letters abcd, 4
bytes (1 byte per letter); the words United States, 13 bytes
(blanks count); a double-spaced, typewritten page, 1500 bytes;
this book, 600,000 bytes (approximately).

Depending on which version of DOS you're using, and whether your
drives use one or both sides of a diskette, your diskettes hold
from 163,840 to 368,640 bytes.  For convenience, quantities the
large are usually given in kilobytes, or K.  One kilobyte equals
1024 bytes, so the capacity of your diskettes can range from 160K
360K.