There are many different kinds of computers. The ones that most people use are called Personal Computers (PCs). Smaller computers that are about the size of a briefcase are called laptops or notebooks. There are also new computers out that are the same size, but they have no keyboard. Text (letters and numbers) is written directly on the screen, these are called Tablet PCs. PDAs are computers so small that you can hold them in one hand. Notebooks, PDAs, and Tablets have batteries so that you can use them where there is no power. They use LCD screens because LCDs are thinner and take less power, so the batteries will last longer. There are also much more powerful computers called mainframes that can be as big as a room or a house!