A personal computer is the most revolutionary communications tool since the printing press.

It is a labor saving device, a research source and an organizer.

It is the basic transportation vehicle on the information highway. Virtually everything you want to know is out there, either in cyberspace or on a disc.

You will probably spend most of your PC investment on hardware. But it is the software that really should drive your purchase decisions. If you want word processing and basic Internet access, for example, any entry-level PC will more than serve your needs. If you want to edit digital video, you'll need a far more powerful machine.

Software & Hardware

A computer uses two types of software - called programs.

The operating system is a built-in program that controls the computer's automatic functions, like your brain controls breathing and blood flow. Windows is the operating system on most personal computers. Macintosh computers use Apple OS (Apple operating system). You may have heard of DOS (disk operating system), a hugely popular early PC operating system rarely used anymore. Other operating systems include Windows NT, Unix, Linux and Gnome.

Application programs give computers instructions to perform specific tasks, like writing letters, creating spreadsheets, calculating taxes and connecting to the Internet. Personal computer users interact directly with application programs, using a keyboard and mouse.

PC users may interact with the computer's operating system to update settings (a new printer, a faster modem speed, change the time on the built-in clock, etc.) but most of these automatic functions are usually set once and then left alone.

The core hardware component inside your PC is the central processing unit (CPU) - the brain of the computer where the bulk of computing occurs. This matchbox-sized unit is connected to various data storage devices, including a fixed hard drive and at least one drive that uses removable media - usually a floppy drive or a CD-ROM drive. Together with a power supply, a modem, a handful of ports to connect external devices and a fan to keep it all cool, these are contained inside a cabinet as small as a book or as big as a carry-on bag.

Computer memory is measured in bits and bytes. A bit is one character of information, a 1 or 0. A byte is eight bits, the piece of information a computer recognizes at one time, like a word.

Bytes are counted by the thousands, in kilobytes. A million bytes is a megabyte, or MB. The standard floppy disk can hold 1.4 megabytes, which represents thousands of pages of text. A CD-ROM can hold more than 650 megabytes, and a DVD can hold 17 gigabytes (17,000 megabytes - or 17,000,000,000 bytes).

Hard drives can hold from 20 megabytes to a dozen gigabytes - millions of pages.

Peripherals enable you to input and output data from the CPU. These include the monitor, the keyboard, the printer and the mouse.

The principal measure of the CPU is the processor chip clock speed, measured in megahertz. The fastest personal computers now run at 750MHz, but in a few years, that may be considered tortoise-like.

Tech talk

A computer recognizes only two opposite states expressed in the 1s and 0s of binary code: "on" and "off." A computer must perform calculations extremely quickly for your command to translate into an on-screen reaction.

Each binary number is a called a bit, short for Binary digiT.  Each single piece of information consists of an eight-digit binary code called a byte, or BinarY digiT Eight. A so-called eight-bit computer can handle any one of the 256 possible combinations of binary code at one time.

This is a limited set of combinations, however. Most PCs contain either 16- or 32-bit processors, which increase the size and complexity of the mathematical representations that a computer can recognize. There are some 64-bit processors, but not yet in use on personal computers.

The expanded capability of faster processors makes a computer easier to use.

Purchase

Once you know what you are going to use your computer for, it will be easier to answer these questions:

• Which computers will work best with the software you need?
• Which operating system is best for you?
• How much memory should your computer have?
• Do you want a desktop computer, a laptop, or a smaller computer?

Ask your dealer for demonstrations and take your time. Your peace of mind is worth a few extra days of exploring your options. Besides this Web site, try some of these sources of information:

• Newspaper columns, books and magazines. Read directories and reviews of software and look over software publisher's catalogs.
• Your friends and business associates.
• Courses offered by computer retailers and local schools.
• How-to videos for sale or rent.
• Computer shows. Check with computer retailers or newspapers for dates.
• Your child's school. Talk to the teacher in the computer lab.
• Check computer manufacturers' Web sites, or call for literature.
• Visit a user group (a club of people who own the same model and share information about it). Computer retailers have lists of them.

A computer can be sold in pieces or as a complete system. The basic price in ads is sometimes for the processing components only. A keyboard, mouse, monitor, printer and even basic software may be extra. Ask the salesperson what's included before you jump at a computer "bargain."

Recognize that what works for you today may not meet your needs tomorrow. Many people rationalize paying a lower price by saying "this is all I need," only to be frustrated later by not having bought enough memory or a fast enough processor.

Generally, it's easy and inexpensive to add memory chips. But processing chips are often the most expensive components in your entire system. And each new generation of computers will be faster than the previous one. It is usually smart to buy a more powerful machine to be sure it will meet your future needs.

Clock speed affects how fast a processor performs, measured in megahertz. Speeds of 400 to 500 MHz are common in today's personal computers. Speeds above 600 MHz are considered extremely fast.

The amount of RAM in your computer is important when you consider the software you plan to run. A sophisticated operating system can use a high percentage of your available RAM, limiting the number of other applications you can have open at the same time. For instance, if you have 32 megabytes of RAM and your operating system needs 20 MB to operate, that leaves only 12 MB for other software applications - plenty for word processing, but maybe not for graphics.

Before you buy a computer, it is a good idea to know what software you will need - operating system and applications - and how much RAM each consumes when running.

Application software and your data files are stored on the hard drive. Application software can require more space in RAM for operating than in storage. For instance, word processing software may require 15 MB to run in RAM, but only 5 MB to store the complete application on your hard drive. Application software lists minimum requirements on the box.

Often a computer is equipped with a math co-processor, a second internal processor that speeds up large spreadsheet operations or calculations in number-crunching such as engineering, drawing, speech or music software.

Many computers contain additional slots that accept chip sets - PC cards - for specific functions that expand a computer's usefulness. For instance, most computers require a card to display full-motion video like a television. Most computers have at least one expansion slot; some offer as many as seven.

A computer has ports on the outside of the cabinet for attaching peripherals. Different peripherals require different types of ports. A monitor, printer, keyboard, modem and external disk will all require their own ports. Make sure your computer has enough and the right kinds.

Ordering by mail is popular because the prices are attractive, software is loaded at the factory and today's components are easy to connect. But don't sacrifice after-sale service to save money. Check whether a facility near your home will service the computer, or if you have to return it to the factory. Be sure to get the same product warranty as if you bought it in a store, and make sure you understand the company's return policy.

Most hardware and software suppliers offer toll-free technical support for their products. Some have better reputations for customer service than others. Ask an objective source.

Connections

Where you install your computer matters. Leave yourself plenty of space for your printer, disk drives, manuals, reference books and disks.

Ergonomics are important. If your keyboard is too high, or your chair too low, you will be uncomfortable after a short time at the computer.

Another consideration is lighting. Your computer screen reflects direct light, making it difficult to read. Avoid fluorescent lighting, which is highly reflective.

Your computer is sensitive to power surges and interference caused by air conditioners, washers, hair dryers and other appliances. Choose a circuit that has no other appliances plugged into it if you can.

Try not to place your computer in a carpeted room. Static discharge can damage sensitive circuits and microchips when you touch your computer. Static electricity can even wipe out or scramble data on your magnetic disks. If you have carpeting in the room, get a plastic floor mat for the computer area.

Place your computer near a phone outlet to use the modem.

Surge & Spike Protection

Your computer, printer and disk drives all have separate power supplies. Integrated circuits and memory chips are extremely sensitive to sudden changes in voltage, which could erase memory and severely damage the internal circuitry.

You can protect them by plugging all your equipment into a power strip with surge protection. A surge protector even shields your computer from lightning and power interruptions.

Depending on how often you experience power spikes (when light bulbs glow or dim suddenly) and how often your power goes off, consider a universal power supply (UPS). This device contains a large battery and circuitry that switches the computer from AC to DC power within milliseconds when it detects a surge or spike.

The battery in a UPS can give you enough time to save your work on a disk and conduct an orderly shutdown of your system.

Ergonomics

Research has found that people who work long hours at computers have fewer backaches and wrist disorders if they use ergonomically built furniture and maintain good posture. This is easier if the furniture and equipment heights are correct.

The most important piece of computer furniture is your chair, which should be comfortable and provide lumbar support. You will be spending a great deal of time in this chair and you'll be more efficient if you are comfortable.

Make sure your desk or table brings the monitor to eye level when you are seated. With your feet on the floor, back against the backrest and screen at eye level, check to see that your forearms are at a 90-degree angle to your upper arms, your wrists are level when you place your hands on the keyboard and your thighs are parallel to the floor.

Consider wrist rests - pads that support your wrist as you type or move your mouse.

Cables

There are three basic types of connective cables: parallel, serial and USB, each with specific applications. Each cable type plugs into an appropriate jack, called a "port," on your computer.

Parallel is a limited one-to-one cable (only one device per port), usually used for older printers.

The more common serial port allows you to "daisy-chain" peripherals. Many printers, scanners and external disk drives have "in" and "out" serial ports that allow you to connect one to another. Each serial device has a "driver," software that allows the computer to recognize it.

A Universal Serial Bus (USB) device can be connected or disconnected with no need to turn off your PC, as you must with serial devices. This type of "hot" connection is appropriate for portable equipment like digital cameras and hand-held computers.

Notice that the connectors on the ends of computer cables have a number of pins in them. Each pin is connected to a wire that runs through the cable to carry a digital signal. Shielding keeps out interference from fluorescent lights or office machines that sometimes disrupt data flow.

When you buy accessory connector cables, look for the word "shielded" and EIA (Electronic Industries Alliance) on the label. If you want the best quality, look for braided cable.

Cables between your CPU and peripherals can be a mess. On your floor, they can cause accidents. A cable management system collects cables together neatly inside conduits.

A vinyl cover can protect floor cables and reduce the chance of tripping over them.

Speakers

Most PCs can output stereo from the Internet, video games and CDs. Your computer can be equipped with small hi-fi speakers - or a multimedia speaker package consisting of two satellite speakers and a subwoofer with built-in amplifier.

Computer speakers are close when you work. Nearfield technology was developed to adjust for the proximity and spread out the soundfield to create a fuller stereo sound.

Disability Aids

There are Braille keyboards and printers for the vision-impaired, monitors with large-print screens, and software that enlarges images on regular monitor screens.

Speech synthesizers also open up the use of computers to the vision-impaired. These programs "read" on-screen text and translate it into spoken words. They "hear" your spoken words and translate them into text. Once reserved for government use, speech recognition software has been perfected and is now available at low cost.

For the hearing impaired, telecommunications devices for the deaf or TDDs (long used on telephones) can be connected to many computers using a special modem and software. A computer network named Deafnet provides a bulletin board and electronic mail service.

There are monitors with touch screens that make it possible to use computers without keyboards. This technology is becoming popular for games and at-home shopping as well as for those who have difficulty typing.

With a graphics tablet and light pen, you write longhand instead of using a keyboard. Advanced handwriting recognition software translates your handwriting into typed text.

An eye-gaze device uses a small infrared light on a headset to relay instructions to the computer.

Maintenance

Keep your computer free of dust and dirt, extreme heat or cold, moisture and static electricity. Keep a dust cover over your monitor, keyboard, printer and disk drive when they are not in use. Exact-fit covers are available for most computers and peripherals. You can even get a keyboard cover that stays on while using the keyboard.

To clean the covers of your computer and peripherals, avoid household cleansers, ammonia, powders and other abrasives and cleaning fluids. These cleansers cause scratches and some can damage plastic.

Instead, clean the keyboard occasionally with commercially available saturated pads or a static-free cloth and cleaning fluid. Do not use any cleaning fluid containing Freon. Spray the fluid on the cloth, not on the keyboard.

Pick up dust and lint between keyboard keys and inside your printer with a computer vacuum cleaner, which comes with a small nozzle and brush. Or clean the keyboard and printer with swabs dipped in a special cleaning solution. Pinpoint a fine stream of air into hard-to-clean places with a compressed air duster.

Remove tobacco smoke, dust, pollen and other pollutants from the air with an electronic air cleaner. Dry air promotes static electricity, which is bad for your computer. Use a humidifier to keep some moisture in the air. Make sure air can circulate freely around the computer and peripherals. A ground wire or a static-control pad or floor mat is a sure way to eliminate static. If static is not a big problem, try static-control strips you stick right on your keyboard.

Only a trained service technician who knows how to avoid safety hazards should touch your computer's internal works. Disk drive recording heads may require cleaning after every 40 hours of drive use, or about once a month if you use your computer frequently.

Many retailers and manufacturers offer service contracts that pick up after your initial warranty period ends. Almost all computer repairs, especially interior circuit boards, are expensive. Given the sensitive nature of the equipment, you may be glad you opted for the service contract.

The toughest aspect about caring for a computer is keeping up with advances in technology. An older computer might continue to perform adequately, but when you try to install new software or a new peripheral, you may encounter a compatibility problem. Ask lots of questions before you buy; let the salesperson know exactly what hardware and software you're currently using.

Consider joining a user group, which provides help from others who use your computer software.