What Is Tablet PC?

I want to know about tablet PC and technologies which are used in this device. Why Tablet PC is not more popular like iPhone.

Yes, I know this is an old post, I’m trying to clean up older posts that are unanswered.
Did you ever figure this out?

A tablet personal computer (PC) is a cross between a laptop or notebook computer and a personal digital assistant (PDA). It's essentially a flat-panel portable computer. The user either taps on the screen with his or her finger or with a stylus, or he or she uses a stylus to write on the screen. A tablet PC can wirelessly connect to the Internet and other computers. The term "tablet PC" originally referred to a specific brand or tablets that were compatible with certain operating systems, but any tablet-sized computer has come to be referred to in some instances as a tablet PC.
The main feature of a tablet computer is portability. These devices typically are about the size of a thin book — roughly 7 to 8 inches (17.8 to 20.3 cm) wide by 9 to 10 inches (22.9 to 25.4 cm) tall and about 0.5 inches (1.27 cm) thick or less, although some might be slightly larger or smaller. They usually weigh less than 2 or 3 pounds (0.9 or 1.36 kg). Their size makes them convenient for businesspeople, students and just about anyone else to take with them in whatever they use to carry their belongings, such as a briefcase, backpack or purse.