A little more than a year ago, the computer industry came up with a new category of device: the "netbook."

Smaller than an ultra-portable laptop and designed primarily for Web surfing and e-mail, the hope was that these light-duty machines would carve out a new market sector as consumers' second- or even third-tier PCs — the equivalent of the kitchen TV.

Ironically, netbooks sales instead took off, thanks to the sluggish economy, and now threaten to cut into the margins of higher-end laptops. The computer industry may have succeeded in unintentionally cannibalizing its own products.

The day after market-research group NPD announced some of the first blockbuster numbers for netbook sales, I sat next to a college student on the train who was actually using one.

It was the Hewlett-Packard Mini-Note. She'd paid just under $300 for it, had had it for more than a month and was just raving about it.

"I tried them all, and this one had the biggest screen and the best keyboard," she said. "On some of the others, the keyboard was squished."

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Netbooks can best be described as low-priced sub-notebook computers with limited storage, connectivity and functionality. Most of them use Intel's Atom processor and have built-in Wi-Fi but neither CD nor DVD drives.

When they first were unveiled in late 2007, many industry analysts were skeptical, to say the least.

At the low end, the machines were challenged by the expanding functionality of smartphones. At the high end, they were challenged by the shrinking size of full-function notebooks. One colleague even likened the genre to the Pet Rock.

But the new numbers from NPD prove conclusively that if it's a rock, it's getting a great roll.

In the first months of 2008, netbooks were less than two percent of laptop sales. By December, that had shot up to 12 percent of total unit volume — and accounted for almost two-thirds of the sales increase in the entire laptop category.

Now, instead of wondering about whether there's a place for netbooks, analysts worry that they'll make a sizable dent in the overall PC market, and, because of their low price point, also cut into profit margins for computer companies hard-hit by the economic downturn.

So what's in a netbook, and who can really make use of them?

The devices themselves have screen sizes of roughly 7 inches to 10 inches; they have USB ports, multi-card slots and most have an Ethernet port.

Onboard memory generally stops at one gigabyte (GB). Storage starts at a tiny 4 GB Flash-based solid-state-drive (SSD) and goes up as high as 160 GB with a traditional hard drive. Most come loaded with variants of either Windows XP Home or Linux.

Netbooks are making significant inroads in the education market. The student sitting next to me on the train was writing a paper using research and class notes she'd previously entered. She used an external CD/DVD drive to load software like Microsoft Office, and a flash drive to move documents around from her netbook to her desktop.

Netbooks also seem ideal for people whose primary need while traveling is Internet access, which the netbooks handle well. I recommended one to a friend who's never owned a computer but asks her acquaintances to look things up on the Web and admits she'd like to start using e-mail.

Most netbooks are small enough to fit in a big handbag or a small briefcase. They fit comfortably on the tray table of cramped airliners, and will be even more useful now that some airlines are offering onboard wireless Internet service. And they're certainly easier to type on than a smartphone's tiny keyboard.

All Netbooks Are Created Equal ... but Some Are More Equal Than Others

We looked at six different netbook models, though with their nameplates covered you might be hard pressed to tell one from the next.

Most were built around Intel's Atom processor; some used SSDs, others regular hard drives. None came with a CD/DVD drive, though all had slots for SD memory cards, standard USB ports, built-in Webcams and Wi-Fi. Most had Ethernet ports and VGA connections for external monitors.

Here's a brief rundown:

Dell Inspiron Mini 9, $299 and up, depending on configuration

Dell's smallest netbook uses a 1.6 GHz Intel Atom processor originally designed for smartphones and other portable devices. It weighs a mere 2.3 pounds, has a smallish 8.9 inch screen and a slightly reduced keyboard (about 12 percent smaller than a standard keyboard). It also comes with a rather petite 8 GB SSD rather than a hard disk drive. Ports include a multi-card reader, 3 USB ports and a VGA port.

The unit we looked at came with Windows XP, but you can also get it with a Dell variant of Linux. That may be fine for Web surfing but could create problems if you needed to share it with Windows-configured peripherals.

Battery life is advertised as four hours, not quite the cross-country flight standard, but certainly more than what you'll need to surf at Starbucks. Nevertheless, with a built-in Web cam and Wi-Fi, the Mini 9 could be the perfect solution for inveterate Web surfers.

Asus Eee PC 900, $250 and up

Taiwan's Asus was one of the pioneers in the netbook category. Its Netbook Eee PC 900A-WFBB01, like the Dell, uses a 1.6 GHz Intel Atom processor (other models come with the older Celeron processor), an 8.9-inch screen, 3 USB ports, a multi-card reader and a VGA port, but is marginally lighter at 2.2 pounds.

It comes preloaded with either Windows XP or a variant of Linux, and has 1 GB of onboard memory, a 4 GB SSD, a Webcam and an Ethernet port. The machine also comes with a foam padded sleeve to protect it from bumps and scratches.

Its major shortcoming was its cramped keyboard, which made it hard to type. The Asus officially comes with a 12-month warranty, but the company claims its real policy is lifetime support on all its products.

Lenovo Ideapad S10, $314 and up

The display on Lenovo's entry, at 10.2 inches, was slightly larger than those of the Asus or the Dell, but the entire machine weighed a modest 2.4 pounds. Like the other two, it uses the Intel Atom processor and has Wi-Fi, a VGA port and a multi-card slot, as well as an Ethernet port, a Webcam and one PCI Express card slot.

Standard internal memory is only 512 MB, but the Ideapad does come with an 80 GB hard drive and a nifty "instant-on" function that allows quick access to the Internet even before a complete Windows boot. The standard operating system is Windows XP Home, and once again, there's no CD/DVD drive.

MSI Wind Megabook U10, $349 and up

The MSI Wind U100 from Taiwan's Micro Star International sports many of the same features as its competition: an Atom processor, Wi-Fi, Ethernet, VGA port, 3 USB ports, a multi-card slot and a Webcam.

It also has one of the wider screens, at 10.2 inches, which allows for a more comfortable keyboard. It uses a traditional 80 GB hard drive, which gives it slightly less battery life some of the others in the field, but then again you get a real amount of storage. It comes with Windows XP Home Edition. For the fashion conscious, the machine is available in six different colors.

Acer Aspire One A150-1570, $314 and up

The Acer Aspire One was one of the early entries into the netbook category. Like the Dell and the Asus, it has an 8.9-inch screen, yet the keyboard didn't feel quite as cramped. Our review unit came in a stunning shade of royal blue (pictured here) though it's also available in white.

This model had a 120 GB hard drive, though 160 GB is available. It has a Webcam, Wi-Fi and the usual assortment of ports and connectors: a PCI express slot, a multi-card slot, VGA, Ethernet and 3 USB ports.

One feature of the Aspire that took some getting used to were the buttons for the touchpad, which are on the right- and left-hand sides instead of below it as usual. Our unit came with Windows XP Home, though you can get it with Linux instead. It also comes with a carrying sleeve that will protect it from scratches, but there's no padding.

HP Mini 1000 Series, $329 and up

At the Consumer Electronics Show in Las Vegas earlier this month, Hewlett-Packard was running around showing off its special Mini-Note 1000, customized by fashion designer Vivienne Tam and costing $699 — as much as a decent full-featured laptop.

For those willing to forgo style for function, you can also get the Mini 1000 for less than half that price. It has a 10.2-inch screen and lays claim to the biggest keyboard in the genre, about 95 percent of full-sized.

It also claims to be only 0.99 inches thick, though I'm still more comfortable calling that "one inch." As with the Acer, the touchpad buttons are on the side. The ports and connectors vary slightly from the competition: Webcam, Wi-Fi, 2 USB port, a multi-card slot and Ethernet.

There's no VGA connector, though HP does provide a connecting slot for a proprietary port replicator. Like the competition, it uses Intel's Atom processor and comes standard with Windows XP. Finally, it has an attractive metal enclosed speaker grille that runs pretty much the width of the machine.

The Bottom Line

When all is said and done, all six of these machines will get you where you want to go if your goal is Web surfing, note-taking and e-mail. These machines aren't desktop, or even laptop, substitutes, but they can do a great job if you understand their capabilities and limitations.

There's a clear tradeoff between the drive size and battery life, with the smaller capacity SSDs getting more from the battery than the traditional hard drives. I like to move my documents around, so flash memory for my document storage does fine for me.

Do I have preferences? Yes, but they are based on my limitations and not the performance of the machines. I have lousy eyesight, so I prefer the machines with the 10.2-inch screen. I have big hands, so I like the bigger keys.

As with everything else, there's a lot of personal preference in choosing one of these machines. If you decide to go for a netbook, just make sure you're getting one for the limited job they're meant to do.