Copyright (c) ZEAK and Associates, 1990 This is the first of a two part article attempting to de-mystify DOS. WHAT IS DOS? You're the proud owner of a new computer and you've picked up one or two programs like a word processor or a spreadsheet to use. But...what is this thing called DOS? Why do you hear so much about it, why have books been written about it, and why have hundreds of pages of instructions been written for it? DOS IS A PROGRAM (SOFTWARE) DOS is a special sort of software. Odds are that none of your other software (programs) would work without it, because DOS controls every part of your new computer system. DOS not only makes it possible for your other programs to work, it also gives you complete control over what your computer does. DOS is the link, the interface, between you and your computer. To appreciate the role DOS plays, let's take a quick look at the various pieces of your computer system and what they do. HARDWARE MAKES IT POSSIBLE The computer equipment is called hardware. It probably includes a keyboard, display (monitor), printer, and one or more disk drives. The purposes of the first three are pretty obvious: You type instructions at the keyboard, and the system responds by displaying or printing messages and results. The purpose of a disk drive isn't quite so initially obvious, but it's purpose becomes clear as you use the system: A disk drive records and plays back information. Some types of IBM (and compatible) computers are listed a the end of this article. The computer's information is recorded in files on disks and you'll find that disk files are as important to your computer work as paper files are to the work you do in an office. SOFTWARE - THE STUFF THAT MAKES IT HAPPEN It doesn't matter if you have a basic system or the latest, high powered 80486-based computer on the market, it can't do anything without software. There are two main kinds of software (programs): 1. System programs, which control the operation of the computer system. 2. Application programs, which perform more obviously useful tasks, such as word processing. Each program must be able to receive instructions from the keyboard, display and print results, read and write files from and to a disk, send and receive data through the computer's communications connection, change the colors on a color display, and so on through all the capabilities of the hardware. All application programs have the same needs. So each program doesn't have to perform all these functions for itself, a system program called the operating system manages the hardware. The operating system allows an application program to concentrate on what it does best, whether it's moving paragraphs about (word processor), tracking accounts receivable (spreadsheet), or calculating stress in a bridge beam (scientific problem solver). DOS is an operating system. The initials stand for Disk Operating System. DOS IS A DISK OPERATING SYSTEM The operating system for many computers, including IBM personal computers (and look-a-likes named clones), is the Disk Operating System. It is called a disk operating system because much of its work involves managing disks and disk files. There are two popular versions of DOS marketed. They are PC-DOS published by IBM, Inc. and MS-DOS published by Microsoft, Inc. They are the same in most ways, but do vary in the features are made available and how they operate. Generally speaking, it's best to use PC-DOS on true IBM equipment and MS-DOS on compata=ibles (clones). Other companies publish versions of DOS to be used specifically on their brands of equipment, but IBM and Microsoft are the most well known. An operating system plays a role something like a symphony conductor. When the score calls for the French horns to play, the conductor cues them. When the score says the drums should play more softly the conductor instructs the drummer. The players in the orchestra and their instruments represent the hardware. The experience and skill of the conductor represent the operating system. The score represents an application program. When one score is replaced by another...Moon River is put aside to be replaced by Handel's Messiah, the same musicians use the same instruments at the same conductor's directions. The elements are all the same, but the outcome is different. When an accounting program (score) is put aside and replaced with a data base program (score), the same hardware (instuments) carries out the instructions of the same operating system (conductor). A different program, different results. DOS coordinates the computer system, just as the conductor coordinates the orchestra. Your application programs run while DOS keeps the system humming. Much of what DOS does, such as how files are stored on a disk or characters are printed on the printer, is invisible to you. You control the things you care about, such as which program to run, what report to print, or what files to erase. DISK DRIVES Personal computers use two types of disks. 1. A flexible disk in a protective plastic jacket, called a diskette, which you can remove from the drive, and 2. A permanently mounted platter called a hard disk. There are two types of diskettes. One is 5.25 inches square in a flexible plastic jacket. The other measures 3.5 inches square in a rigid plastic shell. A hard disk holds from 15 to 100 times as much as a floppy diskette (even more) and it writes and retrieves information a lot faster than a floppy. Most personal computers have either one hard disk and one diskette drive, or two diskette drives. DISK FILES...DATA CABINETS Just as paper files organize and store most written office records, computer information is organized and stored in disk files. A disk file (usually just called a file) is a collection of related information stored on a disk. A file could be a letter, an income tax return, or a list of customers. It could also be a program, because the programs (software) you use are stored in files. Files are involved with almost all computer work. BUT WHY DIFFERENT VERSIONS OF DOS? DOS has been revised a number of times since its initial release. The first version was numbered 1.00. Each revision of DOS is capable of doing more things than the one before it, or newer versions are released to fix problems in the previous one. Ways are found to take advantage of more sophisticated hardware. Each time you start up your system, DOS displays the version number that you are using. If you want to know what version of DOS is installed on your machine, type "VER" on the command lind and press the enter key. DOS will display the version number. When a new version of DOS appears, a change in the number following the decimal point (3.20 to 3.30, for example) marks a minor change that leaves DOS substantially the same as the previous version. A change in the number preceding the decimal point marks a major change. Version 2.00, for example, offered almost three times as many commands as version 1.10. Even though newer versions may have much more capability, they remain compatible with earlier versions. This means that if you start with version 2.1, you can still use all your knowledge and experience, plus all your files and diskettes, when you move to a newer version. All you'll have to learn are the commands and features the new version has added. COMPATIBILITY - WHAT DOES IT MEAN, WHY DOES IT MATTER? You may have seen the terms "DOS-compatible" or "IBM compatible" used in an article or advertisement. Just what does compatible mean? Although some technical issues are involved, the most meaningful measure of compatibility is the extent to which you can use the diskettes from one system with another. If two systems are totally (100%) compatible, you can freely exchange diskettes. This situation is common among IBM-compatible computers now, but was a severe problem in times past. If two systems are incompatible, you cannot exchange diskettes because neither system can read files stored by the other. That's why you can't use a diskette from an IBM Personal Computer in an Apple computer. If two systems are partially compatible, you can interchange some diskettes, particularly those that contain files of information (data). This last level of partial compatibility is what is usually meant by the terms "MS-DOS compatible" and is one of the advantages of using an operating system that runs on so many different machines. YOU CAN DO A LOT WITH DOS! DOS coordinates the operation of the computer for your application programs. That's valuable, but DOS has much more to offer. You can use DOS, controlling it with instructions called commands, to manage your files, control the work flow, and perform useful tasks that might otherwise require additional software. For example, DOS includes a program called Edlin that lets you create and revise files of text. Although it's not a word processor, Edlin is fine for short memos and lists. Using Edlin, you can write short documents in less time than it might take to start your word-processing program and store the file. You can tailor DOS to your specific needs by creating powerful commands in batch files made up of other DOS commands, and you can even create your own small applications. For example, you could create a simple file manager (a program that lets you search a file for specific information) using nothing but DOS commands. Your knowledge of DOS can range from just enough to use a single application program to mastery of the full range of capabilities in the later versions. But no matter how far you go, you don't have to learn how to program. You can do fine just using DOS. Next month we'll put these things we've discussed into practice. Also, we'll offer a summary of the different types of IBM and compatible computers from the venerable PC to the newest dream...the 80586. Written by Eugene A. Zeak, Jr.