How Tablets Work

If you were to crack open a tablet computer to take a look inside, you'd notice three things pretty quickly. First, you've just voided your warranty. Second, the manufacturer has packed all the tablet's components together to create a snug, efficient fit. And third, most of the components you'll see are similar to what you'd find in a standard computer.

The brain of a tablet is its microprocessor. Typically, tablets use smaller processors than full-fledged computers. This helps save on space and cuts down on heat generation. Heat is bad for computers -- it tends to cause mechanical failures.

Tablet computers typically draw power from a rechargeable battery. Battery life for tablets varies between models, with eight to 10 hours being the average. Some tablets will have replaceable batteries. But others, like Apple's iPad and iPad 2, don't allow you to switch out a battery without taking it to a store or voiding your warranty.

Depending on the manufacturer, a tablet computer may be underpowered on purpose. Computer CPUs execute commands in clock cycles. The more clock cycles a CPU runs per second, the more instructions it can process. Some tablets have underclocked processors, meaning the CPU is set to run fewer instructions per second than it's capable of executing. The reason for making a CPU underperform on purpose is to reduce heat production and conserve battery life.

While you might be irritated to learn your new tablet isn't performing at full speed, the truth is most tablets don't need the extra processing power. Programs for tablets tend to be less complex and robust than computer programs. The common term for these programs is applications or apps.

Besides the CPU and battery, other components you'll likely find in a typical tablet include:

Accelerometers and gyroscopes help the tablet determine its orientation so that it displays graphics in either portrait or landscape mode. The graphics processor or GPU takes the load off of the CPU when it comes to generating graphics. The WiFi or cellular components let you connect your tablet to a computer network. The tablet may also have a Bluetooth receiver, allowing it to interface with other Bluetooth devices. One thing you won't find in most tablets is a fan -- there's just not enough space.

There are two basic methods of creating touch screens for tablet devices: resistive screens and capacitive screens. Manufacturers have to choose between the two -- they don't work together.

Resistive systems detect a touch on a screen through pressure. Tablets that require a stylus often use resistive screens. But how does it work?

Resistive systems have a layer of resistive material and another layer of conductive material. Spacers hold the two layers apart. When the tablet is on, an electric current runs through both layers. If you put pressure on the screen, it causes the two layers to come into contact with one another. This changes the electrical field for those two layers.

Imagine you own such a tablet and you've decided you want to activate a game. You use your stylus to tap the game icon on your tablet's screen. The pressure from your touch causes the two layers in the resistive system to touch, changing the electric field. A microchip inside the tablet interprets this change in the field and translates it into coordinates on the screen. The tablet's CPU takes these coordinates and maps them against its operating system. The CPU determines that you have activated the app and launches it for you.

Resistive screens can be susceptible to damage. If you use too much pressure, you may cause the resistive and conductive layers to be in constant contact. This will cause the tablet to misinterpret commands. Resistive screens also tend to have poorer resolution than capacitive screens.

A capacitive system also detects changes in electrical fields but doesn't rely on pressure. A capacitive system includes a layer of material that stores an electrical charge. When you touch a conductive material to this screen, some of that electrical charge transfers over to whatever is touching it. But the material must be conductive or the device won't register a touch. In other words, you can use anything to touch a resistive screen to register a charge but only conductive material will work on a capacitive system.

Capacitive systems tend to be more robust than resistive systems since you don't have to press down as hard to register a touch. They also tend to have a higher resolution than resistive systems.

The idea of the tablet computer isn't new. Back in 1968, a computer scientist named Alan Kay proposed that with advances in flat-panel display technology, user interfaces, miniaturization of computer components and some experimental work in WiFi technology, you could develop an all-in-one computing device. He developed the idea further, suggesting that such a device would be perfect as an educational tool for schoolchildren. In 1972, he published a paper about the device and called it the Dynabook.

The sketches of the Dynabook show a device very similar to the tablet computers we have today, with a couple of exceptions. The Dynabook had both a screen and a keyboard all on the same plane. But Key's vision went even further. He predicted that with the right touch-screen technology, you could do away with the physical keyboard and display a virtual keyboard in any configuration on the screen itself.

Key was ahead of his time. It would take nearly four decades before a tablet similar to the one he imagined took the public by storm. But that doesn't mean there were no tablet computers on the market between the Dynabook concept and Apple's famed iPad.

One early tablet was the GRiDPad. First produced in 1989, the GRiDPad included a monochromatic capacitance touch screen and a wired stylus. It weighed just under 5 pounds (2.26 kilograms). Compared to today's tablets, the GRiDPad was bulky and heavy, with a short battery life of only three hours. The man behind the GRiDPad was Jeff Hawkins, who later founded Palm.

Other pen-based tablet computers followed but none received much support from the public. Apple first entered the tablet battlefield with the Newton, a device that's received equal amounts of love and ridicule over the years. Much of the criticism for the Newton focuses on its handwriting-recognition software.

It really wasn't until Steve Jobs revealed the first iPad to an eager crowd that tablet computers became a viable consumer product. Today, companies like Apple, Google, Microsoft and HP are trying to predict consumer needs while designing the next generation of tablet devices. While it may have taken time to hit the ground running, it seems likely we'll be seeing tablet computers on store shelves for years to come.

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