What's the optimal size of a personal computer? That's a question PC makers wrestle with all the time when designing new models, and it's a question every PC buyer should consider as well.

The trend is clear: small. For the most part, stationary desktop PCs as well as portable PCs have gotten smaller over time-one exception to this is the size of monitors, which has increased.

When taken to an extreme today, you wind up with a handheld computer, also called a palmtop computer. Taken to an extreme in the future, we'll likely have fully functional, voice-activated, talking computers embedded in our wristwatches, clothing, and eyeglasses.

Futurists even write of computers being embedded in our bodies and, eventually, when science truly marries science fiction, the melding of carbon and silicon as hybrid beings evolve that are part human and part robot.

For now, the more mundane and more practical issue is how small you should go when buying a new computer device for work, play, or both.

A relatively new category of computer devices, netbooks, adds a new option. Also called mininotebooks or subnotebooks, these are the smallest computers available today; they have keyboards that you can type into with both hands for quick data entry. Unlike notebook PCs, they don't typically include a CD-ROM/DVD drive.

The name "netbook" came into use because these devices are ideally suited for using web applications. Instead of running programs that reside on your computer's own hard drive, you run programs over the internet that reside on server computers elsewhere. Google Docs (http://docs.google.com) is the best known.

Netbooks as a product category are only about 2 years old, emerging in late 2007, though some contend that netbooks first came into existence in 1999 with the Psion netBook, a device that never caught on. Today's netbooks have caught on, comprising nearly one-fourth of all portable PCs sold, according the latest report by the market research firm DisplaySearch (www.displaysearch.com). Compared with a year ago, netbook sales revenue grew a whopping 264%.

The attraction of netbooks is clear. Compared with other laptop computers, they're lighter, run longer on battery power, and cost less. The main negatives are the flip side of the positives. The smaller keyboards are more difficult to type on, and the smaller screens are more difficult to read.

Some analysts have speculated that the netbook boom will end when the economy recovers, removing some of the attraction of their low price, which ranges from about $250 to $500. But market research firm iSuppli Corp. (www.isuppli.com) predicts that netbooks' popularity will continue to rise, with shipments projected to quadruple over the next 4 years.

According to the latest testing by Consumer Reports and PC World magazines and the online sites CNET (www.cnet.com) and NetbookReviews.com (www.netbookreviews.com), top netbook brands include those by Acer (www.acer.com), Asus (http://eeepc.asus.com), Gateway (www.gateway.com), HP (www.hp.com), and Toshiba (www.toshiba.com).

I tested netbooks by Acer and Gateway. The Gateway LT3103u is typical of larger netbooks, while the Acer Aspire One AOD250-1042 is typical of smaller ones. The Gateway has an 11.6" screen, 2 gigabytes of memory, and a 250-gigabyte hard drive; the Acer has a 10.1" screen, 1 gigabyte of memory, and a 160-gigabyte hard drive.

I liked the Gateway better, but I'm a dyed-in-the-wool desktop PC aficionado, preferring faster typing and easier viewing over the convenience of a smaller size. The Gateway is available from Gateway's site for about $400; the Acer is available from retailers such as Wal-Mart for about $250.

Most netbooks come with Windows XP as their operating system, though you can find them with Windows Vista, Windows 7, and Linux. The MacBook Air is Apple's answer to the netbook trend, but it's considerably pricier than Windows or Linux netbooks.

Here are some observations from regular users of netbooks that I picked up from perusing various online discussion groups: Netbooks are good for just about anything except video editing. Typing speed increases with keyboard size, and typing error rate decreases. You're more likely to take a netbook with you when you're out casually than a notebook. A netbook is convenient even if you rarely or never take it out of the house, e.g., moving it from room to room.

According to what I've observed, younger people take to netbooks more easily than bifocal folks. If you're used to texting on an iPod or a cell phone, a netbook will seem positively roomy. But if you want to optimize ergonomic comfort and safety as well as speed and efficiency when working, nothing beats a full-size stationary desktop computer.