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How the Apple iPad works

Dig into the technologies underlying today's hottest gadget

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Like the iPhone before it, Apple's new iPad tablet is a technological powerhouse with a multitouch-screen interface, an accelerometer that senses movement and tilt, an antiglare screen you can view from a side angle, a long-lasting battery and more.

To uncover how the iPad works, you could dismantle the device and void the warranty. Instead, let me explain the embedded technology.

Apple declined to comment for this story, but I've done some digging and gathered information - and some best guesses - from various sources. I'll skip the hardware novelties that already exist on the iPhone, such as the oil-resistant screen coating and the accelerometer (those are covered in my previous article "How the iPhone works"), and give you the scoop on four under-the-hood technologies that, combined, make the iPad unique -- for now.

Snappy performance for apps

Most reviewers have noted the iPad's impressive speed and responsiveness. When reading e-books, browsing websites, flicking through photos and even playing racing games, I've found that the iPad feels more like a true laptop than a netbook, albeit for one single app at a time. The iPad feels so snappy because of the way the processor delivers performance when needed.

At the heart of the iPad is the 1-GHz A4 processor, which Apple custom-designed for long battery life and quick, punchy performance. "These processors integrate an ARM core, a graphics accelerator and peripherals on a single chip, and they integrate the chip and DRAM into a single package," says Martin Reynolds, a Gartner analyst. (Apple has not confirmed that the A4 has an ARM core, but experts widely agree that it's the likeliest base for the chip.)

Because the iPad does not multitask (meaning you can't open multiple applications at once), the new system-on-chip processor is a perfect fit. The A4 runs more like a high-speed train along a single track than like a car that can easily handle both city traffic and highways. It is not designed to intelligently manage multiple applications and memory loads, but to provide the speed required for a single app.

"The trade-off with system-on-chip is power -- due to the high level of chip integration, plus lots of power management tricks -- versus performance," says Loyd Case, a well-known computer expert, analyst and tech writer. "Since the first iPads won't multitask, raw performance probably won't be a major concern."

With system-on-chip processors, Reynolds says, "most of the data processing is done in a physically small space, which reduces power consumption and increases performance. The short paths and integrated peripherals compensate for the relatively low performance of the ARM processor. Couple that with Apple's optimised software, and you get the responsive environment that Apple needs."

Reynolds explains that the iPad's relatively large battery can dissipate heat better than smaller batteries. This allows Apple to use a processor that generates more heat and runs faster without causing battery overheating - a problem when a smaller battery takes up a confined space. Early tests have shown the iPad to run native applications about twice as fast as the iPhone 3GS.

While the A4 is built for low-power use, the chip is fast enough for most tasks because it is an ARM processor and uses a multibus architecture, says Stephen Lingle, an engineer at Product Development Technologies (PDT), a product design and development firm in Lake Zurich, Ill

What's more, the A4 can manage internal buses, then - like other ARM processors - enter a sleep state in a split second to save power. Conversely, the typical Intel computer chip, such as a Core i5 or i7, is geared for pumping out many simultaneous computations, such as those required for updating a spreadsheet or figuring out polygon locations in a game. A computer processor does not enter a sleep state quite as quickly.

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.


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