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DOS stands for Disk Operating System. DOS is the Operating System, on most PCs, that controls the primary input and output of your computer while you use an application program such as your word processor or database.


DOS performs 2 functions:
1. Links the Hardware; 2. Allows for file management

First, it enables the hardware devices to properly communicate with each other. It is a set of instructions so that the computer's brain understands how its arms and legs operate (keyboard, monitor, printers, etc.). We take this ability for granted. It is like starting a car - many complex systems must work in unison for it to work, yet we take it for granted that it will start.

The second function of DOS is also important. We must have a means to manage the files that we save on our Floppy Disks or Hard Drives. There are times when we wish to copy these files from one disk to another, erase them, or determine which files are on a disk. These tasks are performed often and the software required to do so is DOS.


When you access DOS, you will see the lonesome C:\> prompt on your hard drive.

This symbol signals 3 things:

1. DOS has been properly loaded into RAM
2. "C" is the DEFAULT drive
3. DOS is awaiting your next DOS file management command

Each disk drive and hard disk has a letter associated with it. If a drive is considered the DEFAULT drive, then the computer will always assume that the information needed is in that drive, OR if something you have created is saved, it will be saved to that drive UNLESS you tell the computer otherwise.

All types of disks contain files. We use DOS as a software tool to manage these files. We not only tell the computer which file we want to erase or copy but also which drive it is currently in.

If A:\> is on the screen it is the DOS prompt and in this case the A: drive is the DEFAULT floppy drive which will be searched for information if you issue a command and ask DOS to execute it.

You can CHANGE the default drive simply. Let's try switching drives.

At C:\> try the following example: (Example) A: <press enter key>

The result on screen is now A:\>

The computer now pays attention to A: (A drive). Hopefully there is a disk in A: drive or DOS gets confused and will give you an error message.

Since you have a hard drive (which is usually the C: drive,) you can try switching back and forth between your A: drive and C: in a similar manner. Try switching around between drives, go back and forth a few times. Switching drives is a VERY IMPORTANT SKILL, since DOS pays attention to the default drive whose letter is displayed on your screen.


A filename consists of the name and its extension. Files can be typed in upper or lower case, DOS doesn't care! The file extension frequently gives a clue as to the nature of the file.


123.EXE The program 123, an "executable" file. Think of as a program that can be started and "run" to do something.
GO.BAT A Batch file (bat). Like an exe file. Contains plain english DOS commands and can be viewed with the DOS "type" command.
VIEW.COM Unknown file, but a "command" type, similar to an exe file.
783.WKS A worksheet file from lotus possibly from July of 1983 (7/83)
ME.TXT Probably a text file in plain english. Can be read and viewed with the DOS command: TYPE
XVC.DBF Unknown file, but we might guess a database program database file.
CONFIG.SYS A PC system file. Helps "configure" your computer for specific hookups, and equipment.


CD disks have a relatively limited capacity to store files - limited in comparison to the seemingly expansive space on a hard drive. To find a necessary file name on a CD, just use the DIR or directory command. However, on a hard disk things get a little out of hand with hundreds of files all listed on the same screen. A solution is obtained by adding subdirectories and pathnames to manage the location and organization of file storage. A path is nothing more than a "trail" or "direction post" which helps DOS find a particular file out of the hundreds which may be located on a hard drive.

This pathname is facilitated by the use of multiple directories (called subdirectories) on a single disk. In this fashion you sort files into groups in a specific place on the drive. By the way, a subdirectory is itself a small file and does occupy space on the disk.

You could compare a hard or floppy disk to a department store. The store might sell toys, books and clothes. Similar items go in the same department or area.

A disk also has the capacity for many separate areas in which to place files. DOS refers to these with a main central directory (root directory) and subdirectories branching below it. You can create a subdirectory named TEXT which contains all your word processing documents. Computer utilities could be in a subdirectory called UTIL, and so on.


- ? and * - DOS can use "wildcards" in many operations (? *).
Simply stated, these wildcards take the place of letters and numbers. Use the question mark as any SINGLE character. Use the * as any GROUP of ANY LENGTH of characters. Think of them as shortcuts to get the job done! Very powerful and useful! Frequently used with the COPY and DEL commands which are discussed in a few paragraphs.

Example: C>dir A:*.wks

Means provide a directory listing of any files on the A: drive ending in WKS and beginning with ANY characters of ANY length from 1 to eight digits. Files such as MY.WKS or NUMBERS.WKS or NAMES.WKS would fit this description.

Example: B>copy ???.dat A:
Means copy any files to A: drive ending in DAT and having any characters in the filename AND ONLY filenames exactly three digits long.

The often used *.* means ANY FILE NAME and ANY extension regardless of length.

For instance: Example: C>copy *.* A: (means copy ALL files from the existing default C: into the A: drive)

C>copy A:*.* B: (means copy ALL files from A: to B:)
A>del finance.* (delete files from the A: drive which begin with finance and have ANY file extension size or character type.)
A>Copy *.DOC B: (All files with the extension DOC)
A>Del S*.* (Any file that begins with the letter S)
A>Del B:*.* (ALL files from the B drive - be careful!)
A>Dir B:*.COM (A list of all files with an extension of COM on the B drive)


Many of the DOS commands once loaded stay inside the machine. These commands stay resident (stay put) and are called INTERNAL commands. DIR is an example of an INTERNAL COMMAND - it lives inside the computer once DOS is loaded.

EXTERNAL COMMANDS only live on disk (Hard or Floppy) and can be copied to other disks (example: FORMAT.COM). They load TEMPORARILY into the computer memory, do their job and then are gone. EXTERNAL DOS COMMANDS MUST HAVE A DOS DISK OR DIRECTORY (OR COPY) of that command in a disk directory or drive when you need them.

The following are examples of some useful DOS commands:

- DIR - (Internal) means "directory" (a list of files or programs on the disk.)You get a listing of files in the drive (hopefully a disk is in the drive.) Notice that we added /p to the end of a command.

C> Dir (List all files)
C> Dir A: (List on files on diskette)
C>dir/p <enter> Show a list of all files and "pause after each screenful."

- COPY - (Internal) copies one or several files to a disk or directory. Copy can duplicate a file onto another disk or into a subdirectory (more on subdirectories later). Copy is a very flexible and powerful DOS commands. Use the copy command with the wildcards seen above for even more flexibility.

Example: B>copy zip.doc A: (copy zip.doc from B: drive to A: drive.)

Example: A>copy B: (copy from C: drive to B: drive.)

Example: C>copy C:fuss.txt B:whine.txt (copy fuss.txt from C: drive to B: drive and rename it whine.txt)

Remember, if the computer is not told differently, it will assume the DEFAULT
A>COPY A:sample.wk1 B: is the same as:

A>COPY sample.wk1 B:

The "A:" in the first example is redundant.

- DATE and TIME - (Internal) A calendar and clock exist within DOS. On some computers it automatically is updated and kept current. Date and time data is important to DOS since it is attached to all files to keep track of when they were created so you can determine which file is most recent.

Example: B>time Example: A>date

- DEL or ERASE - (Internal) deletes files or groups of files.
Use DEL*.* to erase all files from a disk. See our previous mention of wildcards (* and ?). Deleting old files is a necessary operation, though, which frees up space on a disk.

Example: A>del whine.txt Example: B>del 784.jid

Example: A>del *.jid (notice the use of the * wildcard we mentioned earlier!)

Example: A>del old.* (notice the use of the * wildcard we mentioned earlier!)

- DISKCOPY - (External) copies entire contents of one floppy to another.
Diskcopy is a wise idea since disks wear out after several hundred hours of operation. All information on the target disk will be destroyed and over-written with the new information, so be careful!

Example: A>diskcopy A: B: (copy the contents of A: floppy to B: floppy)

- CLS - (Internal) clears the screen and puts the cursor in the home (upper left) position. Useful. Try it!

Example: A>cls

- CD or CHDIR - (Internal) changes the current (active) subdirectory or directory. CD\ brings you to the root (main directory) no matter where you are.

C> CD\WINDOWS (Change to Windows directory)
C> CD\ (Change to the root directory)

- FORMAT - (External) Prepares a blank floppy to receive data. Format erases any old files on a disk - be careful! Format prepares the tracks and sectors which will receive the data. All disks must first be formatted prior to use.

Example: B>format A: (format floppy in A: drive)

Example:C>format A:/s (format floppy in A: AND add system files)

Tip:DANGER! If you enter any of these commands, your files are off to Computer Heaven, never to be seen again.
A>format C: wipes out your hard drive!
Also C> del *.* wipes out hard drive.

- SCANDISK - (External) This is an advanced disk utility. It will check the disk and highlight any problem areas. It uses a Graphical User Interface.


B>rd\letters\financial (removes financial subdirectory below letters subdirectory and root directory)
A>md data (make directory data)
Example: A>cd\ (change to the root or uppermost directory)

Example: C>cd\data (change to subdirectory named data below the root)


A>DIR B:/P - Displays list of files one screen at a time

A>DIR B:/W - Displays list of files using the entire width of the screen

A>COPY A:filename.ext B: - To copy one file from Disk A to Disk B

A>DEL B:filename.ext - To remove the specified file from the specified drive.

A>DISKCOPY A: B: - Making an exact copy of the diskette in Drive A onto the diskette in Drive B. (Follow on-screen directions)


1. State the uses of 5 Internal commands and 5 external commands.

2. What is the difference between Internal and External commands?

3. Explain the following: Directories, Format, Rename, Path, Full pathname.

4. Give 5 specific and original examples of the use of wildcards.

5. Name the 5 most important DOS commands and state why they are important.

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