The most familiar computer is the desktop version. But computers now exist that are as small as pocket calculators and as powerful as many large desktops were just a few years ago. These smaller personal computers come in five basic configurations, designed to be used outside the home or office:

• Laptop
• Notebook
• Hand-held (HPC)
• Palm
• Electronic organizers

Hand-helds, palm and electronic organizers are often grouped into a category called personal digital assistants (PDAs).

Portable computers include specialized features for away-from-home situations, but few are designed for the heavy-duty use a desktop provides. Most portable computer keyboards are smaller than a desktop keyboard, making touch-typing more difficult.

PDAs do best for such applications as scheduling, storing phone numbers and addresses and reading e-mail.

Electronic books provide interactive access to information, but since the user cannot input data, they are not really "computers."

Features

All portable computers have CPUs; a screen; both RAM and storage memory; a keyboard; ports for adding printers, modems and larger; external monitors; and ports to connect to other computers.

Some laptop computers can be used in place of a desktop for those with limited space, but most portable computers are designed to supplement a desktop. Hand-held and palm PCs are designed to connect to a primary desktop machine to synchronize data between the two.

All portable computers operate by battery, but most also run off AC while recharging the internal battery.

In addition to the main power battery, many portable computers require a flat "button" battery to maintain memory integrity and back-up personalized system configurations while the main batteries are changed.

Laptops

Laptop computers are sophisticated enough to be your primary computer, especially if you travel extensively or if space at home is a problem. The case is hard plastic to protect the computer from the bumps and bruises of travel. A laptop opens like a briefcase; the top half houses the screen, the lower half contains the keyboard and cursor control. Varying ports and plugs are aligned around the keyboard base.

Laptops usually weigh less than 10 pounds and are generally less than two inches thick. Their screens are usually around 12 inches measured diagonally, depending on the model.

A laptop's cursor control is either a track button or a "scratch pad" - a flat surface you run your finger across to move the cursor. There are peripherals designed specifically for use with laptops, including modems, floppy drives and CD/ ROM drives.

Some external hard drives are configured to fit into a laptop's battery compartment.

Many laptops add or substitute disk drives or ports with PC card slots. PC cards, about the size of three credit cards stacked, are available for a variety of applications.

Many airports also require you to prove that your laptop computer is really a laptop computer, and will ask you to turn it on before boarding.

A security note: When flying, never check your laptop as baggage. It's a tempting target for sticky fingers.

Notebooks

A number of diminutive computers, smaller than laptops, are grouped into the notebook category. Generally if they are the size of a school notebook or smaller, they still can run a full version of Windows.

The major difference is the lack of CD-ROM or floppy disk drives, and the keyboard is smaller than standard - a concession to the size of the notebook.

But notebook computers offer the power and operational flexibility of a desktop or laptop computer in a much smaller package.

Hand-helds

The primary differences between notebook computers and hand-held computers are not their size but the way the cursor is manipulated and the operating software they run on.

Because hand-helds (HPCs) are so much smaller - with 5- or 8-inch screens - filling them with the power and flexibility of a full-blown operating system would be expensive. So instead of running Windows, HPCs operate on a version of Windows called Windows CE (consumer electronics), which doesn't require as much memory. Windows CE also is designed to sync with a desktop computer when connected by a serial cable and running corresponding software on a desktop PC.

HPCs are just about pocket-sized and are designed as a supplement to a desktop computer. Instead of a mouse, HPCs have a touch screen. A built-in "pen" or stylus is sometimes used.

The savings in power, weight and size lowers the cost, with most HPCs costing less than half the price of laptops.

Palm PCs

These calculator-sized devices give you an organizational tool and electronic date book.

The most striking aspect of palm PCs is their lack of a keyboard. Palm PCs use a touch screen and stylus, but also include handwriting recognition software, which turns handwritten print into computer-recognizable type.

Palm PCs measure approximately 3 x 5 inches and less than an inch thick, with a touch screen measuring 2.3 inches x 3.2 inches. A palm PC's buttons provide direct access to date book/calendar, to-do list, address book and, sometimes, a notepad. Many palm PCs also have memory chip recording, similar to digital telephone answering machines, to quickly capture ideas or reminders.

Although many palm PCs use a version of Windows CE, the dominant palm operating system is not Windows-based, but one called Palm Pilot. The Palm Pilot and Windows CE environments are incompatible.

Additional software can be downloaded, both versions of familiar desktop software and special applications designed for the palm PC. Palm PCs also have memory card slots into which other hardware can be connected, such as a special palm PC modems.

Most palm PCs have infrared capability that allows similar palm PCs to swap data, such as trading electronic business cards.

Palm PCs synch data to desktop computers via serial cables. 

Electronic Organizers

Electronic organizers are lightweight, pocket size, usually less than an inch thick, and operate on batteries. Each has a miniature keyboard, directional cursor keys and keys for clock and calendar.

You can organize your life with a clock and calendar program, an address/phone directory, low-level database management and minimal word processing. Most can be connected to a modem and to your desktop PC to exchange information.

Electronic organizers are loaded with internal memory, from 8 K to 256 K, and you can add more as you need it. They also store data in flash memory, tiny solid-state storage cards.

Because it is based on simpler technology, an electronic organizer can cost a quarter of a palm PC.

Electronic Books

Although many electronic books resemble hand-held or palm PCs, they really aren't "computers" since they don't allow a user to input and store data.

An electronic book provides interactive access to information in the book's chip. Electronic books are available for bibles, travel guides, sports and movie encyclopedias, dictionaries and foreign language translators. Recently, more popular fiction and nonfiction titles have been put in electronic book format.

Today we can download new "books" from the Internet.