How the iPad Works

Like the iPhone, the iPad is primarily a touch device. The front is dominated by a 9.7-inch (24.6-centimeter) touch screen, with a single button (the same Home button found on the iPhone) placed below it. Apple offers two different iPad colors: one with a black face bezel and one with a white face bezel. The front also houses a webcam for Apple's FaceTime video chatting, while the back has a higher resolution camera for taking better photos. The iPad's build looks more like an iPhone 3GS than the newer iPhone 4 or iPhone 5, thanks to a smooth, curved metal body. A power button sits at the top edge of that curved surface. The iPad's only other buttons sit on the right side of the device: a rocker controls volume, while another button can serve as mute or rotation lock for the screen.

The fouth generation iPad measures 9.5 inches (24.1 centimeters) tall by 7.3 inches (18.5 centimeters) wide and 0.4 inches (1 centimeter) deep. Unlike most Android tablets, Apple has chosen a 4:3 aspect ratio for the iPad instead of the widescreen 16:9. The closer-to-square design keeps the iPad from being awkwardly tall or wide in either portrait or landscape orientation, though the trade-off is that widescreen videos can't make as much use of the screen space. The iPad uses an IPS, or in-plane switching, LCD planel. The viewing angles and colors of IPS displays are superior to standard or twisted nematic TFT screens typically found in notebooks and flat-panel monitors. For instance, the iPad can be viewed clearly from a viewing angle of 178 degrees [source: Brandrick].

While the look of the iPad hasn't changed much from iteration to iteration, it has gotten lighter (and then heavier again). Apple cut the first iPad's 1.5 pounds (0.7 kilograms) down to 1.3 pounds (0.6 kilograms) with the iPad 2. The third and fourth generation models increased that weight a little due to a larger battery. That's a rare move for Apple, but they had a good reason for the increased weight: The third generation iPad introduced a dramatically higher resolution screen to the tablet, which makes content much sharper.

We'll dive into the specifics more on the next page, which is all about the iPad's hardware.

Taken apart, tablets and smartphones look a whole lot like laptops. The same basic components are all there: processor and memory, screen and battery. Of course, there are some key differences between mobile devices and full-size computers. Where your desktop PC likely has a large graphics card that's totally separate from the central processing unit (CPU), mobile devices like the iPad run on systems-on-chip (SoCs). A SoC contains the CPU and GPU in a single, compact unit, which is very power- and space-efficient.

The fourth generation iPad, released in late 2012, runs on the Apple A6X, a 1.4GHz dual-core processor with a quad-core graphics processing unit (GPU) onboard. At the time of its release, benchmarks showed it was the most powerful SoC on the market [source: Extreme Tech].

Other key components of the fourth generation iPad include 1GB of RAM, a 720p FaceTime front-facing cam, 5 megapixel rear camera, a 42.5 watt-hour battery, Bluetooth 4.0, standard sensor package (gyroscope, accelerometer and ambient light sensor) and a digital compass. Of course, every iPad includes a WiFi chip, and Apple sells models with 3G and LTE cellular support. The base model comes with 16 gigabytes of flash storage, but for $100 or $200 more you can upgrade to 32GB or 64GB, respectively.

With the launch of the iPad 2, Apple introduced a new type of cover for the device. The iPad Smart Cover uses magnets to latch on to the iPad and cover it snugly. The cover can be opened and folded into a triangular shape to prop up the iPad 2 and serve as a stand. And once the cover is on the iPad 2, the device switches to sleep mode. The cover helps protect the screen while conserving battery life. The iPad Smart Cover is purchased separately from the tablet itself.

The iPad's standout feature is its screen, and that's especially true with the third and fourth gen models. The first two iPads used a 1024 by 768 pixel display, while the third generation model quadrupled the number of pixels to 2048 by 1536. That's a higher resolution than most computer monitors and HD televisions! Apple has branded its high resolution screens "Retina" displays because the pixels are so small, you can't individually discern them.

But wait, does that mean you're going to have to squint to read anything on the iPad 3 or 4? Nope. The iPad still displays content at the same resolution, but essentially uses four display pixels for every one image data pixel. The increased pixel density reduces aliasing, making text and images smooth and sharp. Apple kept the iPad's resolution unchanged so that apps developed for past hardware would still work just as well on the new screen.

As good as the iPad hardware is, Apple's real strength is iOS, the mobile operating system its tablets and phones run on. Let's take a look at the iPad's user interface and app store.

If you're familiar with the iPhone or iPod touch, chances are you could pick up an iPad and start using it without much trouble. All three devices change picture orientation by simply rotating the device via built-in, three-axis accelerometers. Like the iPhone and iPod touch, iPad has a full QWERTY on-screen keyboard. When the device operates in landscape mode, the iPad's virtual keyboard is almost the same size as keyboards found in iMac systems.

Apple includes a number of basic applications on the iPad, such as its Web browser Safari, its magazine and book app Newsstand, its music store iTunes, and other apps with handy, self-explanatory names: Mail, Photos, Clock, Calendar, Notes, Contacts, Messages, Camera, Game Center. There are more -- far more -- available in the App Store. There are more than 650,000 apps listed in the app store, and more than 225,000 of them are designed specifically for the iPad. Apps designed for the iPhone will still run on the iPad, but they won't look as good on the device's larger screen.

The number of apps available for iOS keeps growing. The mobile operating system continuously changes, too. Apple has kept the same basic look for every version of iOS: Rows of app icons make it simple to access each application. Swiping left or right on the display reveals additional screens of icons, though a dock at the bottom of the screen doesn't change as you swipe between screens (it's there to hold the apps you use the most).

Many other features of iOS have become fairly standard for touch devices. A pinching motion can be used to zoom in and out of photos and web pages. Holding down on apps can be used to delete icons or reorganize them. Dragging app icons on top of one another organizes them into folders. Swiping down from the top of the screen pulls down Apple's Notification Center, a screen that organizes notifications (new e-mail and text messages, alarms, missed calls, and so on).

Games and other apps make use of the iPad's hardware in various ways: Some are controlled by rotating and tilting the device, triggering its motion sensors, while others rely on touch controls like tapping and swiping. The third and fourth generation iPads also support Siri, Apple's "voice assistant" which can be used to control various parts of the device.

Now that we've got a basic grasp of how the iPad works, let's take a look at some of its most common uses. These are the reasons 100 million people have bought iPads to replace (or augment) their laptops and smartphones.

Web browsing. E-mail. Social media. These are the three pillars of the iPad: According to a 2012 study, most people spend their iPad time on those activities [source: Business Insider]. Of course, Web browsing is a huge category. That can include reading up on news, browsing blogs, reading long articles, or looking at pictures of cats. Social media includes services like Facebook and Twitter and chatting with friends via instant messaging.

If you think about it, these uses make sense. The iPad's touchscreen isn't the ideal format for doing lots and lots of typing, but it's fine in short bursts, and some people use the tablet in combination with a keyboard attachment. Web browsing dominates nearly 40 percent of iPad use, while e-mailing and social media take up the next 20 percent. Games and video watching each get around 12 percent. Many people use their iPads while in bed or on the couch. It often becomes a secondary media device -- a way to catch up on Facebook and Twitter while watching TV.

Apple's iBooks and the Amazon Kindle app both provide access to large libraries of books. Many people use the iPad as an e-book reader. Other services, like Instapaper, are designed with devices like the iPad in mind. Instapaper allows you to save Web pages for later reading and strip them down to a simple, easy-to-read text layout.

The iPad and other tablets have dramatically affected Web design since 2010. More sites are being built to look great on tablets and mobile devices, and the concept of separate mobile sites is slowly being replaced by flexible designs that work on multiple screen sizes. This speaks to the heart of what the iPad is best at: consuming content. While there are thousands upon thousands of apps in the app store, few of them focus on creating content. There are options, like drawing apps and Apple's own Garage Band for creating music, but touchscreens lack the precision of mice and keyboards for creative work.

As Apple releases a new iPad approximately once per year, there are a lot of choices out (though they discontinue old models, plenty are still for sale used). We'll lay out the different versions of the iPad.

Every iPad has WiFi, but Apple also sells versions of the iPad with 3G and LTE wireless capabilities. The cellular models are more expensive, and you'll also have to pay a carrier to use data on their network. In the United States, Apple partnered with AT&T and Verizon to offer 3G data for the iPad 2. When they released the third generation iPad with a Retina display, they also added 4G LTE support. AT&T, Sprint and Verizon all partnered with Apple to carry that device.

The WiFi models work much the same way a notebook or netbook computer works. The devices communicate with a wireless Internet connection via built-in WiFi. You would be subject to the same Wi-Fi hotspot limitations with this iPad model as you would a notebook computer. The WiFi plus 3G model allows you more freedom to browse the Internet and check e-mail. By utilizing similar wireless and cellular technology found in the iPhone, you can tap into the Internet using 3G service, but it'll cost you. If you go this route, not only will you pay a higher price for the 3G-enabled device, you'll need to purchase a data plan through AT&T or Verizon.

Since January 2010, Apple has released four iterations of the iPad. The fourth generation system notably added a faster processor and replaced Apple's 30-pin dock connector with a new port that it calls Lightning. The much smaller Lightning port was introduced in the iPhone 5 in fall 2012. Otherwise, it's identical to the third generation system which added the Retina display -- commonly called "the new iPad" in Apple's marketing. Both "the new iPad" and the original iPad from 2010 have been discontinued, but the iPad 2 is still on sale. It's cheaper, priced at $400, and lighter than the fourth generation iPad. It's lighter because it has a much smaller battery -- Apple had to nearly double the capacity of its battery to support the demanding high resolution screen.

Apple lists a comparison of all currently available iPad models on its Web site. Here are the most important distinctions: The iPad 2 is cheaper and lighter than the iPad with Retina display, but has a lower resolution screen, lower resolution cameras and an older processor. It also uses the 30-pin dock connector, and its cellular model does not support LTE. The newer iPad has the same battery life, supports Siri, has the new Lightning connector, can shoot 1080p video and has a 720p webcam. Most importantly, its A6X processor includes a quad-core graphics chip, making it the most powerful mobile system-on-a-chip around as of late 2012.