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The programs you buy in the box off your dealer's shelves, in person or through the Web, the ones you run to do actual work on your computer, are its applications. The word is actually short for application software. These are programs with a purpose, programs you apply to get something done. They are the dominant beasts of computing, the top of the food chain, the colorful boxes in the store, the software you actually pay for. Everything else in your computer system, hardware and software alike, exists merely to make your applications work. Your applications determine what you need in your computer simply because they won't run—or run well—if you don't supply them with what they want.

Today's typical application comes on one or more CDs and is comprised of megabytes, possibly hundreds of megabytes, of digital stuff that you dutifully copy to your hard disk during the installation process. Hidden inside these megabytes is the actual function of the program, the part of the code that does what you buy the software for—be it to translate keystrokes into documents, calculate your bank balance, brighten your photographs, or turn MP3 files into music. The part of the program that actually works on the data you want to process is called an algorithm, the mathematical formula of the task converted into program code. An algorithm is just a way for doing something written down as instructions so you can do it again.

The hard-core computing work performed by major applications—the work of the algorithms inside them—is typically both simple and repetitive. For example, a tough statistical analysis may involve only a few lines of calculations, although the simple calculations will often be repeated again and again. Changing the color of a photo is no more than a simple algorithm executed over and over for each dot in the image.

That's why computers exist at all. They are simply good at repeatedly carrying out the simple mathematical operations of the algorithms without complaining.

If you were to tear apart a program to see how it works—what computer scientists call disassembling the program—you'd make a shocking discovery. The algorithm makes up little of the code of a program. Most of the multimegabyte bulk you buy is meant to hide the algorithm from you, like the fillers and flavoring added to some potent but noxious medicine.

Before the days of graphical operating systems, as exemplified by Microsoft's ubiquitous Windows family, the bulk of the code of most software applications was devoted to making the rigorous requirements of the computer hardware more palatable to your human ideas, aspirations, and whims. The part of the software that serves as the bridge between your human understanding and the computer's needs is called the user interface. It can be anything from a typewritten question mark that demands you type some response to a multicolor graphic menu luring your mouse to point and click.

Windows simplifies the programmers' task by providing most of the user interface functions from your applications. Now, most of the bulk of an application is devoted to mating not with your computer but with Windows. The effect is the same. It just takes more megabytes to get there.

No matter whether your application must build its own user interface or rely on the one provided by Windows, the most important job of most modern software is simply translation. The program converts your commands, instructions, and desires into a form digestible by your operating system and computer. In particular, the user interface translates the words you type and the motion of your arm pointing your mouse into computer code.

This translation function, like the Windows user interface, is consistent across most applications. All programs work with the same kind of human input and produce the same kind of computer codes. The big differences between modern applications are the algorithms central to the tasks to be carried out. Application software often is divided into several broad classes based on these tasks. Table 3.1 lists the traditional division of functions or major classifications of computer application software.

Table 3.1 Basic Types of Computer Application Software

Class of Software


Web browsers

Entering and interacting with Web sites and servers to buy, sell, research your favorite interests, and just while away evenings, afternoons, and the rest of your life

E-mail programs

Sending and receiving instant messages from friends, associates, and solicitors in your neighborhood and around the world

Word processors

Getting your words write for print or electronic publishing


The accountant's ledger made automatic to calculate arrays of numbers


A filing system with instant access and the ability to automatically sort itself

Drawing and painting programs

Creating and editing images such as blueprints and cartoon cels that can be filed and edited with electronic ease

Multimedia software

Playing MP3 and WAV files for music, showing AVI or MOV video files, playing games, or displaying images and sound like a movie theatre under the control of an absolute dictator (you)

The lines between many of these applications are blurry. For example, many people find that spreadsheets serve all their database needs, and most spreadsheets now incorporate their own graphics for charting results.


Several software publishers completely confound the distinctions by combining most of these application functions into a single package that includes database, graphics, spreadsheet, and word processing functionalities. These combinations are termed application suites. Ideally, they offer several advantages. Because many functions (and particularly the user interface) are shared between applications, large portions of code need not be duplicated, as would be the case with standalone applications. Because the programs work together, they better know and understand one another's resource requirements, which means you should encounter fewer conflicts and memory shortfalls. Because they are all packaged together, you stand to get a better price from the publisher.

Today there's another name for the application suite: Microsoft Office. Although at one time at least three major suites competed for space on your desktop, the other offerings have, for the most part, faded away. You can still buy Corel WordPerfect Office or Lotus SmartSuite, although almost no one does. (In fact, most copies of Office are sold to businesses. Most individuals get it bundled along with a new computer.) Office has become popular because it offers a single-box solution that fills the needs of most people, handling more tasks with more depth than they ordinarily need. The current version, Office XP, dominates the market because Microsoft sells it to computer makers at a favorable price (and, some say, with more than a little coercion).


Even when you're working toward a specific goal, you often have to make some side trips. Although they seem unrelated to where you're going, they are as much a necessary part of the journey as any other. You may run a billion-dollar pickle-packing empire from your office, but you might never get your business negotiations done were it not for the regular housekeeping that keeps the place clean enough for visiting dignitaries to walk around without slipping on pickle juice on the floor.

The situation is the same with software. Although you need applications to get your work done, you need to take care of basic housekeeping functions to keep your system running in top condition and working most efficiently. The programs that handle the necessary auxiliary functions are called utility software.

From the name alone you know that utilities do something useful, which in itself sets them apart from much of the software on today's market. Of course, the usefulness of any tool depends on the job you have to do—a pastry chef has little need for the hammer that so well serves the carpenter or computer technician—and most utilities are crafted for some similar, specific need. For example, common computer utilities keep your disk organized and running at top speed, prevent disasters by detecting disk problems and viruses, and save your sanity should you accidentally erase a file.

The most important of these functions are included with today's computer operating systems, either integrated into the operating system itself or as individual programs that are part of the operating system package. Others you buy separately, at least until Microsoft buys out the company that offers them.

Common utilities include backup, disk defragmenting, font management, file compression, and scheduling—all of which were once individual programs from different publishers but now come packaged in Windows. Antivirus and version-tracking programs are utilities available from separately from Windows.

Modern utilities are essentially individual programs that load like ordinary applications when you call on them. The only difference between them and other applications is what they do. Utilities are meant to maintain your system rather than come up with answers or generate output.


An applet is a small software application that's usually dedicated to a single simple purpose. It may function as a standalone program you launch like an ordinary application, or it may run from within another application. Typically the applet performs a housekeeping function much like a utility, but the function of an applet is devoted to supporting an overriding application rather than your computer in general. That said, some system utilities may take the form of applets, too. Applets are mostly distinguished from other software by their size and the scope of their functions.

When you download a page from the Web that does something exciting on the screen (which means it shows you something other than text that just lays there), it's likely you've invisibly downloaded an applet from the Internet. Applets let you or distant programmers add animation and screen effects to Web pages.

Other applets are often included with or as part of application software packages (for example, the "wizard" that leads you through the installation process). Some are included with operating systems such as Windows. In fact, the chief distinction between an applet and a full application may be little more than the fact that you don't buy applets separately and never have.

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