The magazine of the Melbourne PC User Group
A Beginner's Tale: Part 3
Ron Wilby

Last month I promised to divulge some of the secrets, so important for beginners, that I found in the paperback, PC D0S. My ex-colleagues told me, "DOS is the operating System everybody uses" and I had decided learning about DOS was next on my list. Here are some of the things I learned.

What is an Operating System

An operating system provides the interface between you and your computer. It executes the commands you enter from the keyboard and manages the system resources such as disks, printer, mouse, etc. The operating system allows you to run other programs, called Application Programs, such as word processors, databases, and spreadsheets. What are they? I'll try to find room to explain as we go along.

Sometimes, though, DOS hides behind a secondary program that takes control of the computer soon after startup. This is known as a 'Shell' and commands are issued from a screen, called a menu, on which several alternatives are displayed for you to select.
 
Even if you have a shell, I strongly recommend you get behind it and learn a little about the basics of Dos. That's what I did. I'm not proposing to make you into Dos experts [leave that to Tom Coleman) but only into adequate users of Dos.

BIOS

When switched off the computer is dead. There is nothing in memory. Dos is hanging about somewhere on hard or floppy disk, but is powerless. Before the operating system can operate we need something to start the whole thing, something to breathe life into this dead computer. That something is called the BIOS (stands for Basic Input Output System) and lives on an EPROM chip that is part of the computer. When you switch on the power your BIOS is ready and waiting and performs POST (Power On Self Test). POST checks that your hardware is in working condition, and you will see on screen messages from the BIOS in the first half-minute or so after power-on. Also during this time you will be able to use a Set-Up program to configure the way your computer operates. My advice is don't. Leave that to the experts, at least until we can make you into an expert

Booting 

After the POST routine (about half a minute) the POST hands over control to DOS. At this point you need a 'System Disk', either a floppy, which must be in drive A, or your hard disk. In those early days I didn't have a hard disk, they were expensive and not so common. So I had to boot up (start) the computer every time from a system disk, then change to the program disk which I wanted to use. In the Institute where I used to work they proudly showed me a 'lab' full of PCs, "one to each class member, and they've got hard disks too!" - one megabyte hard disks! But I digress. DOS looks at drive A first. 

If there is a system disk there, then that disk is used for startup. If the disk is not a system disk, you get an error message telling you its a "non-system disk, replace and try again", or words to that effect if there is no disk in drive A (or the door is open) DOS moves on to drive C, your hard disk. Most PCs are booted from drive C, but be aware that if there is a disk left in drive A, DOS will try to use that first.

When DOS has found a system disk it proceeds to 'boot' your computer, which means that DOS looks at a file called CONFIG.SYS for information about how you want your computer configured and also looks at a file called AUTOEXEC.BAT to find which of various DOS programs are to be 'loaded' into memory after which the computer is ready and willing to adept commands. Later I'll show you how to modify CONFIG.SYS and AUTOEXEC.BAT, but for now you should see on screen the Dos prompt, which will be

A:\ or C:\

followed by a blinking line. 'This line is DOS saying to you, "type your command here, Master". Depending on the exact setup of your machine, you may see a menu offering a number of choices instead of the Dos prompt There will be some command, which may be displayed on screen, to take you from the menu to the prompt. In DOS 5 that command is Alt+F4 (which is a convention for saying, "Press the 'Alt' key and F4 together").

If you are using these writings in learning (not laughing) mode, please get yourself to the DOS prompt. To do that, put your copy of a DOS system disk (never use the original) in drive A, press Ctrl+Alt+Del (that is, press all three keys simultaneously). This will reboot your computer and you should now have the DOS prompt

DOS Commands 

After all that education from my paperback Self-Teaching Guide, PC-DOS, mentioned above, what can I do with it? What you do, I found, is issue (type on screen) commands, which DOS carries out. Let's look at some of those commands.

DISKCOPY

This comes first because, they told me, you should immediately make copies of any program disks you buy. Use the silver or black tabs which come with your box of floppy disks to write protect your original disks (stick the tab over the notch in the side of the floppy) or, if you have 3.5 inch disks, move the write-protect tab over. Now, put your original disk in drive A and at the DOS prompt type DISKCOPY A: B: and press Enter. So I did as I. was told.

Here is where I started to learn an important lesson, to listen to the computer whew it talks to you. It talks, of course, by on-screen messages, and in this case, DISKCOPY has the computer say:

insert SOURCE diskette in Drive A: 
insert TARGET diskette in Drive B: 
Press any key when ready...
Some Things to Note:

  • DISKCOPY will overwrite (destroy) any data on the target disk
  • Dos refers to disk drives as a capital letter followed by a colon, e.g. A:, B:, C: etc. - to DOS 'A' is another keyboard character, in this case capital 'A'. The colon ':' makes 'A' into 'Drive A:'
  • If you have two floppy drives, DOS tells you to put the 'target diskette in Drive B:. If the computer has only one floppy drive DOS will give on-screen instructions which you must follow to make a copy using a single drive, which is Drive A: 
  • 'Press any key when ready ... ' refers to any character key, 'Enter', or the spacebar. The Shift, Ctrl, and Alt keys are all really shift keys and do not behave as 'any key'
  • DOS refers to floppy disks as 'diskettes'. I can't think of anyone else who does, they are usually called 'disks' or 'floppies . I think 'diskette' refers to the days of 8 inch, and even 12 inch, computer disks and lots of flashing lights just like in the movies. Because our present-day disks are much smaller they are called 'diskettes' by DOS.
The Keyboard
A word about the keyboard. Pretty elementary, you think. Well, remember, this is A Beginners Tale.

If you are a typist you will notice the centre of the keyboard is in standard, or QWERTY, form - but there are some special keys.

Most important is the carriage return, which takes you down one line and back to the left-hand margin. It is usually labelled 'ENTER' or just 'RETURN'. Apart from its physical function (moving the cursor to the next line and placing it at the left margin) the Enter key also 'enters' commands - you type your command and then press Enter to have the command carried out, or executed.

The BACKSPACE key usually erases as it backspaces. The TAB KEY has a backwards tab obtained by pressing Shift+Tab. [Ed. Not on all computers, and not within all applications. MK]

FUNCTION KEYS are along the top (or down the left side on older keyboards) and are marked F1 to F12 (F1 - F10 on older equipment), although I have never used F11 and F12. The function keys are shorthand keys, the exact function depending on the particular program you are using. Very often F1 summons help.

ESCAPE, usually labelled 'Esc', means escape and this key is usually used to cancel or 'back out' of a position in a program Dos uses Esc to abandon a command before Enter is pressed.

CONTROL, marked 'Ctrl', is another shift key because it changes the function of other keys when pressed. Usually used with a letter key, so that 'Ctrl+S' means hold down CM while pressing 'S'. This also often written '^S'.

ALT, the 'alternate key marked 'Alt, is another shift key used with a letter in commands the effect of which depends on the program being used.

PTRINT-SCREEN, sometimes labelled 'PrtSc' is used with the shift key (Shift+PrtSc) to send whatever is on the screen directly to the printer - but not always, on most computers BIOS has to be in control for the print screen function to work. It is an esoteric point and not one for beginners to fret about.

INSERT is a 'toggle' key. When in the 'on' condition whatever you type is inserted into the current line (that is, it pushes other text out of the way to make room). With Insert in the off condition new text overwrites old text.

Entering Commands After 'booting' you should see the DOS prompt which, on my machine anyway, is either A:\ or C:\ followed by a blinking line (the cursor). Later, you will be able to change the cursor style or shape. As you type a command it is stored in a special memory, called the keyboard buffer. The command is only sent on to the Command Processor when you press Enter. This gives you a chance to correct any typing mistakes with the Backspace or Esc keys. Backspace erases the character above the cursor, Esc cancels the entire line.

The Default Drive

When the prompt shows A:\ that means the default drive is A: and Dos will use A: to carry out commands and look for programs until you tell it otherwise. To change the default drive, type the name of the new drive (C: or B: - don't forget the colon) at the cursor and Enter: DOS will change to the new drive and the prompt will change from A:\ to B:\ . Your commands will now be carried out on the disk in the B: drive. 

In the next episode of A Beginner's Tale I will have much more to tell you about DOS commands and other fascinating matters. Farewell until then. 

Reprinted from the Jan / Feb 1993 issue of PC Update, the magazine of Melbourne PC User Group, Australia

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