If you've been around computers for a long time, this is what you probably think of instinctively at the mention of a drawing tablet: a plain surface that you draw on with a stylus, with your work displayed on a separate computer monitor. Graphics tablets remain the most affordable drawing tablet category. Their main disadvantage is the sense of ‘disconnect’ between the drawing surface and the screen, although most people get used to this quickly.
Pen displays consists of a flat-screen monitor with a pressure-sensitive surface that you draw on with a stylus. They don't have the sense of disconnect that you might get with graphics tablets, and they're more portable; however they cost more. Furthermore, you get a lot of cables between the display and computer (see the best computers for graphic design), and the display surfaces don’t offer the ‘bite’ that graphics tablets do.