There are many different types of computers. What they all have in common is that they have microprocessors in them that processes the input they receive from the user by means of a mouse or keyboard and displays the results on a screen.
The overall term for all types of small computers is the personal computer which is typically used for general purposes by a single person. Usually this term has been designated for a computer that runs the Windows operating system, but Macintoshes are considered personal computers as well.
One of the types of computers is the desktop computer which has a permanent location on a desk or table. These computers typically offer more versatility and power than a comparable laptop.
A laptop, sometimes called a notebook, is another of the types of computers that is portable and about the size of an average hardcover book but slightly thinner in nature. It contains the same parts that a desktop has including a pointing device, keyboard, display, and hard drive and is usually batter-operated but comes with a power adapter for recharging and use with a standard wall outlet.
There are ultra-portable computers known as netbooks which are even smaller than laptops are priced between $300 and $500. They are extremely cost effective but are less powerful than laptops.
Even smaller than the netbook is the Personal Digital Assistant or PDA which is about the size of a paperback novel and light in weight. It uses flash memory instead of a hard drive for storage and typically has a touchscreen instead of a mouse and keyboard.
There are also very large computers known as mainframes and supercomputers. Mainframes are large computers that were popular about twenty years ago and still exist in some enterprises. Supercomputers are priced in the million dollar range and are used for computations that require large amounts of computing power such as weather forecasting and military applications.