One remarkable reality of the personal computer revolution is that the computers and the components in them continually get faster, smaller, and cheaper. One dilemma this has led to, for many buyers, is deciding just what type of computer to buy when it's time to replace your current one.

The major decision is between a traditional "desktop" computer, which sits atop a desk in your office or home, and a "laptop" computer, also called a "notebook" computer, which can perch on your lap and is not much bigger than a notebook you might tote around with you on the way to a meeting or class. The term "laptop" used to refer to a larger portable computer and "notebook" to a smaller one, but this distinction has largely disappeared.

To complicate matters even further (whoever said computers were easy?), you can choose among different types of both desktop and laptop computers.

With desktop units, big tower PCs are more expandable than mid-tower systems, and this can be helpful for advanced users. Compact systems and all-in-one units are less-expandable still. The latter units integrate the monitor and case and are very easy to set up.

With laptops, "desktop replacements" pack virtually all of the computing power of a desktop system but can still be conveniently transported from one location to another. Ultraportables are for "road warriors" who travel frequently with their machines and can benefit from having to lug around the lightest burden possible. Value notebooks offer a middle ground between the two at lower prices.

One sea change in the world of computers is the increasing feasibility, even desirability, of using any kind of laptop as your sole computing device, whether in the office or home or away from it. Unlike in the past, today's laptops provide all the processing power, memory, and hard disk storage space that most users need at a price premium that's the smallest it has ever been. And the market has responded.

Last year, the market research firm NPD Group made headlines in the computer press by announcing that sales of laptop computers in terms of revenue in the retail market had surpassed those of desktop systems for the first time.
The picture is similar, if not as revolutionary, regarding the total number of units sold. I asked Alan Promisel, an analyst with market research firm IDC, to do some number crunching, and he reported that unit sales of laptop PCs in the U.S. as a percentage of the total market have been increasing: 16.7 percent in 1999, 19.1 percent in 2000, 21.4 percent in 2001, 23.7 percent in 2002, and 27.2 percent in 2003.

Clearly, the trend is up.

Still, despite portability and size benefits, laptops don't make sense for everyone, said Leigh Weber, incoming president of the Independent Computer Consultants Association (http://www.icca.org) and a computer consultant in Maple Glen, Pennsylvania.

Though the price difference is smaller than it has ever been, it could still cost you several hundred dollars for the increased portability and space savings. And though the functionality difference is less than it has ever been, if you're doing high-end gaming or high-end graphics (such as video editing and computer-aided design), you'll benefit from the added capabilities of a desktop unit.

Laptops are also less ergonomic. Some people find themselves slumping over their laptops, which can cause neck and back strain. Some laptops have reduced-size keyboards, which can crimp your hands. If you do a lot of number crunching, most laptop keyboards don't have a separate number pads, which you may find less convenient. Some people don't like the pointing device built into laptop keyboards, which takes some time getting used to and isn't as precise if you do a lot of graphics or drawing.

There are work-arounds for these shortcomings, however. You can add a numeric keypad and external mouse to a laptop, though this makes it less convenient to take it to the next location. You can use a "port replicator," plugging your laptop into it to have access to a larger monitor, keyboard, and mouse.

One wildcard to the above picture is the all-in-one PC, which uses little space, like laptops. Apple Computer, with its colorful iMac, created this trend, and Gateway, Sony, Hewlett-Packard, and others are following suit.

Sales of these "designer" units, which can be as appropriate for the living room as the home office, are projected to increase from 1.2 million in 2003 to 32.1 million in 2008, according to market-research firm Gartner.