That leaves us with the ultra-mobile PC (UMPC). Technically, the term applies specifically to a Microsoft product. It's a tablet computer -- imagine a computer screen without a keyboard. The interface for most UMPCs is a touchscreen with a stylus and an array of physical keys set along the sides of the screen. These tablets tend to be light like netbooks and feature small screens in the 4- to 7-inch (10.2- to 17.8-centimeter) range.
Some UPMC models have a full QWERTY keyboard that you can slide out from under the screen. Others rely exclusively on the touchscreen interface. Most run on the Windows Vista operating system. While UMPCs are more portable than notebooks, they are more expensive than netbooks.
Samsung's Q1UP-XP Ultra Mobile PC is a good example. It has a seven-inch (17.8-centimeter) LCD touchscreen display and weighs just two pounds (.9 kilograms). It has a split QWERTY keyboard with keys on either side of the screen. It's also WiFi and Bluetooth compatible. The computer has a microphone and can serve as a voice over Internet protocol (VOIP) device. The price tag for the Q1UP-XP at the time of this writing is $1,299.
But some people use the term UMPC to describe all small computer devices, including netbooks. Others use it to differentiate pricey mobile computers from inexpensive netbooks. For example, while Apple calls its MacBook Air product a notebook, others say it doesn't fit the notebook category. The Air is thin enough to fit inside a standard manila envelope and features a 13.3-inch (33.8-centimeter) LED backlit display. But its processor is less powerful than other MacBook models. It has limited storage space and only a few ports. The Air also costs a pretty penny: the starting price is $1,799.
The Air's design, processing power and price make it tricky to categorize. That's why some journalists use the term UMPC to describe devices that are portable but are more powerful and expensive than netbooks. Using this terminology, a netbook is small, inexpensive and has modest processing power. A UMPC is small, more expensive and generally has a better processor than a netbook.