Jan's Computer Basics:8-1 System Software

Computer Basics

8 - System Software: Intro

System software is a catch-all term for the programs that handle the running of your computer's hardware. The two main categories are:

operating systems
Screen with logos of operating systems

utility programs
Screen with logos of utility programs

Operating Systems

conductor 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.

Where you are: JegsWorks > Lessons > Computer Basics
	1. Computer Types
	2. Applications
	3. Input
	4. Processing
	5. Output
	6. Storage
	7. Computer to Computer
	8. System Software Intro Functions Types Utilities Quiz
	9. Programming

	10. What You See
	11. Hands On!
	12. On Your Own

	Search Glossary Appendix

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.

Boot screen with AMIBIOS

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 may require 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.

Here is an example of a config.sys that might be used with Windows 95, with explanations in blue on the right. The blue parts can't be in the real file. Win95 doesn't require a config.sys unless there are devices that you want to run in DOS mode.

DEVICE=C:\WINDOWS\HIMEM.SYS /eisa

This device manages the high memory. Very important.

DEVICE=C:\WINDOWS\EMM386.EXE NOEMS

This device manages the rest of memory. Very important.

DEVICEHIGH=C:\PIONEER\ATAPI_CD.SYS /S:3 /D:MSCD001

This device operates the CD drive. The HIGH part says to load the driver HIGH in memory, so the HIMEM device must be loaded too.

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!

Here's an example of an autoexec.bat that might be used under Windows 95, with explanations on the right in blue. The blue parts can't be in the real file. Win95 doesn't require an autoexec.bat but you might want to change some of the defaults or to have some things to run in DOS mode.

@C:\PROGRA~1\NORTON~3\NAVBOOT.EXE /STARTUP	Starts Norton's Antivirus program
@SET TEMP=H:\TEMP @SET TMP=H:\TEMP	These two lines tell programs where to put temporary files
@c:\windows\command\mscdex.exe /d:ATAPI_CD.SYS	Starts driver for CD- ROM
@ECHO OFF	Allows some lines to not show onscreen when this file is run
@PROMPT $p$g	Sets how the command line will look
@SET PATH=C:\WINDOWS;C:\WINDOWS\COMMAND;C:\;	Tells where to look for files when full name with directories is not given
REM This is a remark.	If a line starts with REM the computer ignores the rest. So this is a way to write yourself notes about what the lines do.

The @ in the front of a line keeps that command from displaying on the screen as it is executed. Some people want to see them ALL. Most of us would rather not think about it!

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, 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. See DOS Commands

So we see that without the operating system, the computer is paralyzed. Let's look now at the types and functions of operating systems.

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~~ 1 Cor. 10:31 ...whatever you do, do it all for the glory of God. ~~

Last updated: 22 Jan 2008