GENERAL DOS USAGE SX/DX
As we have explained, DOS controls the flow of information between the various components of your
PC. It also provides you with the tools to organize the information on your disk drives and even check
whether they are working properly. The core of DOS is a file called COMMAND.COM. This file
contains the basic DOS instructions and is loaded into your system’s memory every time you turn on your
computer. When we talk about “booting” your computer, this means [SX/DX 5-3] to turn on your
computer and load the COMMAND.COM. When the DOS prompt appears, this tells you that the
COMMAND.COM file has been loaded and that you can start your computing operations.
Internal Commands
Internal commands are those that are automatically loaded into your PC’s memory every time you boot
your computer. Because they are loaded into memory, they are always available for use even if you have
removed the DOS diskette from your floppy disk drive. These commands are the most frequently used,
and include CLS, COPY, DELETE, DIR, TYPE and VER, all of which are explained later in this
chapter. There are many other internal commands, details of which are given in your DOS user’s manual.
External Commands
External commands are used less frequently, and must be loaded from a disk drive. These commands will
only be loaded into memory when you type the command name, assuming your DOS diskette is inserted
in the disk drive currently displayed in the DOS prompt. For example, if you loaded DOS from your a
drive, then to load a program from the DOS diskette, you simply type the name of the command after the
A> prompt. If the prompt is shown as C> (i.e. the C drive, the hard disk drive, is currently being
addressed) and you type the name of a DOS command while the DOS diskette is in the A drive, you will
see an error message since your PC will not be able to find DOS in the C drive. In this case you would
first have to type A: to change back to the A drive. Later in this chapter the CHKDSK and FORMAT
commands both external commands, are introduced. Full details of all the external commands are to be
found in the DOS user’s manual.[SX/DX 5-4]
Basic Rules
We list here some basic rules for DOS usage, which apply in all cases:
Commands can be typed in either uppercase or lowercase letters, or even combinations of both.
To execute a command the < Enter> key must be pressed after the command has been typed at the
DOS prompt.
To change the disk drive currently being addressed type in the letter of that disk drive followed by
a colon (:).
In order to execute an external DOS command, the relevant command must be present on the disk
drive currently being addressed, as indicated by the DOS prompt.
To correct typing errors when typing in command use the < Backspace> or cursor left keys to
delete the incorrect characters.
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GENERAL DOS USAGE SX/DX
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