Computer makers Acer and MSI Computer on Tuesday introduced sub-$500 mini-notebooks powered by Intel's new Atom processor.

The slightly larger MSI Wind, which stands for Wi-Fi Network Device, comes with a 10-inch display and weighs 2.6 pounds. Acer's Aspire One has an 8.9-inch display and weighs nearly 2.1 pounds. Intel's 1.6-MHz Atom processor powers both computers.

The new computers fit into the category of ultra-portable notebooks, which IDC defines as clamshell devices costing less than $500 and having screens measuring 7 to 10 inches. The notebooks are also lumped together in the industry under the loosely defined category of ultra-mobile PCs or mobile Internet devices.

The MSI Wind, which uses the Intel 945 GMS chipset for graphics and other tasks, includes 1 GB of memory, an 80-GB hard drive, a Webcam, and built-in support for Wi-Fi and Bluetooth wireless technologies. The LED display has a resolution of 1024 x 600 pixels.

The Windows XP version of the Wind has a manufacturer suggested retail price of $499. A Linux-based model is scheduled to ship this summer with a MSRP of $399. The device is available in white, black, or pink.

The Acer Aspire One, which uses Intel's Graphics Media Accelerator 950 chipset, includes an 8.9-inch LED display with the same resolution as the Wind, 512 MB of memory, and Wi-Fi support. The machine does not include Bluetooth support.

The machine is available with either Linux or Windows XP. Pricing starts at $379.

The ultra-portable notebook category started taking off more than a year ago with the introduction of the 7-inch Asus Eee PC, which cost $299. The popularity of the device prompted other manufacturers to jump into the market.

Hewlett-Packard in April introduced an 8.9-inch notebook called the HP 2133 for $499, and Dell has said it plans on entering the market soon. Asus is demonstrating its own Atom-powered 8.9-inch notebook this week at the Computex conference in Taipei, Taiwan.

The most compelling reason to own the small notebooks, which have keyboards too small for much more than e-mail and browsing the Web, is to avoid carrying around a heavier and bulkier regular laptop. The low-cost notebooks offer a true Web browsing experience, which sets them apart from smartphones and other handheld devices.

The smaller notebooks are not expected to attract the majority of consumers, according to IDC. Most of them will opt to pay a bit more for a full-size notebook that will become their only portable. The only market that the research firm sees the ultra-portables used as a primary computer is schoolchildren from kindergarten to the eighth grade.

Worldwide shipments of ultra-low-cost notebooks will grow from less than 500,000 units last year to more than 9 million in 2012, IDC predicts. As a percentage of the total consumer PC market, the devices will remain under 5% through the forecast period.

Intel's Atom, introduced in March, is a low-power processor built specifically for the increasing number of mobile Internet devices, or MIDs. The chip is available in models ranging from sub-watt to 2.5 watts and can scale to speeds up to 1.8 GHz.