How the iPad works

Dig into the technologies underlying today's hottest gadget

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 Web sites, 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 optimized 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 Inc. (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.

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.

Lingle explains how a lithium-polymer battery works in even more basic terms: There is a positive side and negative side, and electrons jump from one side to the other to form a charge. When the chemical is excited by electrical power, the electrons flow through this circuit -- because that is the shortest and easiest path to take -- and eventually the polymer chemical won't be able to make this jump anymore and will stop charging.

According to Lingle, the polymer chemical material in the iPad battery is likely either polyethylene oxide or polyethylene acrylonitrile.

Embedded Web audio and video

Apple CEO Steve Jobs has stated his dislike of Adobe Flash, a multimedia platform that's used widely across the Web, on more than one occasion. The iPhone doesn't support Flash, and neither does the iPad. Instead, the Safari browser found in the new device supports HTML 5, the next iteration (still under development) of the HTML standard.

Like other multimedia platforms, such as Microsoft Silverlight, Flash requires that you install a third-party plug-in to view videos and other rich content on the Web. HTML 5, on the other hand, supports embedded video and audio so you can play them right in the browser without installing a plug-in.

David Stude, a software engineer at PDT, says HTML 5 also supports vector graphics that can scale and shift on the screen during Web browsing, similar to how a table in Microsoft Word can change size depending on the zoom level. Stude says his company has done prototyping for embedded devices -- gadgets like the Chumby or Wiki Reader that act like a computer with an operating system but are self-contained -- with HTML 5 instead of Flash because it is easier to set up software routines.

Flash and Silverlight require proprietary scripting languages, says Stude, but HTML 5 is a one-stop shop for programming rich content into a Web page that anyone can use. While HTML 5 is still years away from being finalized, as an emerging standard it will help developers create apps for all devices that support it, regardless of whether they have a proprietary add-on. In addition to Safari, the most recent versions of Firefox, Opera and Google Chrome provide some support for HTML 5 features, and Microsoft has promised that Internet Explorer 9 will also adhere to HTML 5 standards.

Of course, some view the lack of Flash support as a serious detriment. The majority of interactive elements on the Web today are built in Flash, which means they won't work on the iPad. But Jobs and others are confident that as HTML 5 matures, more Web developers will create apps using HTML 5. In the meantime, Apple is providing a short list of big-name HTML 5-friendly Web sites that work perfectly on the iPad.

Apple likes to use the word "magical" when describing the iPad, and it may feel that way when you're using it. But what seems like magic can be explained with hard science after all.

John Brandon is a veteran of the computing industry, having worked as an IT manager for 10 years and a tech journalist for another 10. He has written more than 2,500 feature articles and is a regular contributor to Computerworld.

This story, "How the iPad works" was originally published by Computerworld.

Copyright © 2010 IDG Communications, Inc.

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