How the iPad works

Dig into the technologies underlying today's hottest gadget

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The A4's straight-as-an-arrow processing speed also provides a boost for games. In Real Racing HD, for example, the photorealistic cars speed along in lifelike fashion because the processor is churning out extra pep just for that app. On other computers and tablets, some processing power is reserved for other tasks.

Note: Apple announced yesterday that limited multitasking abilities will come to the iPad this fall with the upcoming iPhone OS 4. Only certain tasks, such as audio play, VoIP and location tracking, will be able to run in the background while other apps are active. Another new feature will sidestep true multitasking by suspending an app when the user switches to another task, then later resuming that app right where the user left off. We won't know until this fall whether such restricted multitasking will have any effect on the iPad's speed.

Extrawide viewing angle

While it can't match the crispness of the 167dpi grayscale E Ink display found in dedicated e-readers like the Amazon Kindle, the iPad's 1024-by-768 color LED-backlit LCD screen is bright and highly readable. The real wizardry, however, is the IPS (in-plane switching) technology, which provides a 178-degree viewing angle -- meaning the display looks sharp and bright from the sides as well as from the front. IPS displays achieve this because they let more light through the liquid crystals in more directions than do other LCDs.

"This has to do with the way light passes through the color filters in an IPS panel," says Art Marshall, NEC Corporation of America's product manager for professional displays. "If you're looking at an IPS LCD panel lying on its side, the liquid crystals in an IPS panel are aligned horizontally and there is very little distortion of light as it passes through the color filters. Comparing this to TFT [thin-film transistor], where the liquid crystals are organized so that they start turning at near right angles to the substrate, the display allows much more light to pass through."

The wide viewing angle makes the iPad appropriate for browsing the Web with a friend or reading a book while slouched on the sofa.

"The IPS display is relatively rare -- it provides a particularly high level of resolution and should be easier on the eyes than other types of LCD," says Rob Enderle, principal analyst at Enderle Group. However, he notes, "it will still glare out in sunlight [like any LCD screen] and be harder on your eyes for reading than E Ink," because the iPad resolution is lower.

Super-long battery life

Why does the iPad battery last for 10 hours or more? That is one mystery that gearheads have debated for the past few months.

The iPad battery is made from lithium-polymer, which is a more moldable chemical material than the lithium-ion used in most laptop batteries. With a polymer battery, Apple can shape the battery around the iPad, which means the battery is bigger and can hold more ions for recharging.

"All lithium batteries function via the movement of ions back and forth between the electrodes," explains Tim Feaver, CEO of Porous Power Technologies LLC, a company that makes lithium batteries. "When the cell is charging, ions move from the anode to the cathode, and when [the battery is depleted and not charging], the ions move back to the anode again."

The electrodes must be separated from each other by a medium that allows the unrestricted flow of ions back and forth, says Feaver. "This medium is a thin layer, the separator, containing an electrolyte through which the ions move." With a polymer battery, the liquid organic electrolytes are absorbed into the polymer chemical to form a gel, says Feaver.

This gel, says PDT's Lingle, is what makes the polymer moldable and larger than other batteries. The moldable battery lasts longer mostly because there is more space for the chemicals used for charging.

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