Operating systems

Between the hardware and the application software lies the operating system. The operating system is a program that conducts the communication between the various pieces of hardware like the video card, sound card, printer, the motherboard and the applications.

What can a computer do without an operating system?

Not much!! Let's look at what happens when you turn on your computer, before the operating system is involved. The first screen you see when you turn your computer on will be about the BIOS (Basic Input/Output System) of your computer. The BIOS is a set of instructions on a ROM chip (Read-Only Memory) that controls how the hardware and the operating system communicate. It's a very limited set of instructions.

Notice the instruction to "Hit DEL if you want to run Setup.". Other keys might be used for a different brand of BIOS. Don't do this unless you know what you are trying to do. Setup allows you change certain features of your computer at a very basic level, but doing it wrong can keep it from working right or even at all!

An older BIOS might not understand your newest, spiffiest piece of hardware. In this case you would have to get a new motherboard or an updated BIOS. A newer motherboard will have a BIOS that can be updated using software. It requires making a physical change on the inside of your computer, running a special software program, then resetting the motherboard back the way it was. (This is a task only for the brave and technically skilled since you can ruin a motherboard very easily!)

After the BIOS has gone through its morning wake-up routine, you'll see on your screen something about running the POST (Power On Self Test). This is a set of tests of the hardware. If, for example, your keyboard is not plugged in or is broken, you will see a message about "Keyboard failure" and the computer will stop where it is in the POST. There are tests included for the hard drives, memory, and the buses, too. This is only a quick check-up though and does not guarantee that everything is perfect.

That's it for what the computer can do without an operating system. It can wake up and twitch a little, but it can't move or talk yet. Its nervous system is not working.

Next the computer looks for some kind of operating system. It will usually be set up to look in the floppy drive first and then on the hard drive. This way if your hard drive fails, you have a way to get the system working enough to diagnose the problem. Enough of the operating system to get started will fit on a 3½" floppy disk. This part of the operating system has various names. Kernel, master program, supervisor, control program are a few. In PCs using DOS or Windows the term kernel is used.

When the kernel is loaded, the computer looks for three files:

command language interpreter	The command language interpreter is the program that turns your keystrokes into all those 1's and 0's for the processor to swallow. For DOS and Windows 95 the program is command.com.
config.sys	From the config.sys the computer finds what devices are connected, such as a mouse, CD drive, or scanner. The file tells where to look for the directions, called drivers, for using these devices.
autoexec.bat	This file does optional tasks like loading programs that you want to start every time your computer is turned on. You may see a lot of messages on the screen as the various programs are started. This file also tells the computer where to look for files, called the path. Many programs add their own directories to the path when they are installed. The path can get too long to function right!

By the way, if you look on your hard drive under Windows for these files, you might not see them. The default installation of some versions of Windows hides system files, which includes autoexec.bat and config.sys. To view such files you must change a setting. From any My Computer or Explorer window, on the View menu, select Options. Then choose the View tab. There is a choice there to show or not show system and hidden files.

DOS - When your pretty graphical interface breaks, you may have to go to the command line to fix it. Even within Windows 3.x and Win95/98, it can be faster to type a command on the Run line than to find the right icon to start a program. So, a knowledge of DOS commands is not yet useless.