Alternately, an onscreen keyboard can be used where you tap each letter with the stylus. Their pocket calculator size and light weight make them easy to hold in one hand and very portable. On the other hand, if you plan on doing a lot of word processing and internet surfing, you'll need the extra computing power of a handheld. These computers have a clamshell design with a keyboard and usually have a larger screen which is touch sensitive. Some handhelds can be as small as palm units, others the size of a typical paperback.
Professional models are as large as a hardcover book.