How the iPhone Works

Electronic devices can use lots of different methods to detect a person's input on a touch screen. Most of them use sensors and circuitry to monitor changes in a particular state. Many, including the iPhone, monitor changes in electrical current. Others monitor changes in the reflection of waves. These can be sound waves or beams of near-infrared light. A few systems use transducers to measure changes in vibration caused when your finger hits the screen's surface or cameras to monitor changes in light and shadow.

The basic idea is pretty simple -- when you place your finger or a stylus on the screen, it changes the state that the device is monitoring. In screens that rely on sound or light waves, your finger physically blocks or reflects some of the waves. Capacitive touch screens use a layer of capacitive material to hold an electrical charge; touching the screen changes the amount of charge at a specific point of contact. In resistive screens, the pressure from your finger causes conductive and resistive layers of circuitry to touch each other, changing the circuits' resistance.

Most of the time, these systems are good at detecting the location of exactly one touch. If you try to touch the screen in several places at once, the results can be erratic. Some screens simply disregard all touches after the first one. Others can detect simultaneous touches, but their software can't calculate the location of each one accurately. There are several reasons for this, including the following:

Many systems detect changes along an axis or in a specific direction instead of at each point on the screen. Some screens rely on system-wide averages to determine touch locations. Some systems take measurements by first establishing a baseline. When you touch the screen, you create a new baseline. Adding another touch causes the system to take a measurement using the wrong baseline as a starting point.

The Apple iPhone is different -- many of the elements of its multi-touch user interface require you to touch multiple points on the screen simultaneously. For example, you can zoom in to Web pages or pictures by placing your thumb and finger on the screen and spreading them apart. To zoom back out, you can pinch your thumb and finger together. The iPhone's touch screen is able to respond to both touch points and their movements simultaneously. We'll look at exactly how the iPhone does this in the next section.

To allow people to use touch commands that require multiple fingers, the iPhone uses a different arrangement of existing technology. Its touch-sensitive screen includes a layer of capacitive material, just like many other touch screens. However, the iPhone's capacitors are arranged according to a coordinate system. Its circuitry can sense changes at each point along the grid. In other words, every point on the grid generates its own signal when touched and relays that signal to the iPhone's processor. This allows the phone to determine the location and movement of simultaneous touches in multiple locations. Because of its reliance on this capacitive material, the iPhone works only if you touch it with your fingertip -- it won't work if you use a stylus or wear non-conductive gloves.

The iPhone's screen detects touch through one of two methods: Mutual capacitance or self capacitance. In mutual capacitance, the capacitive circuitry requires two distinct layers of material. One houses driving lines, which carry current, and the other houses sensing lines, which detect the current at nodes. Self capacitance uses one layer of individual electrodes connected with capacitance-sensing circuitry. Both of these possible setups send touch data as electrical impulses.

The 2012 iPhone 5 replaced the previous touch screen with an in-cell touch screen that still uses capacitive multi-touch technology, but combines the capacitive touch sensing layer and the LCD display layer into one.

The iPhone's processor and software are central to correctly interpreting input from the touch screen. The capacitive material sends raw touch-location data to the iPhone's processor. The processor uses software located in the iPhone's memory to interpret the raw data as commands and gestures. Here's what happens:

1. Signals travel from the touch screen to the processor as electrical impulses.

2. The processor uses software to analyze the data and determine the features of each touch. This includes size, shape and location of the affected area on the screen. If necessary, the processor arranges touches with similar features into groups. If you move your finger, the processor calculates the difference between the starting point and ending point of your touch.

3. The processor uses its gesture-interpretation software to determine which gesture you made. It combines your physical movement with information about which application you were using and what the application was doing when you touched the screen.

4. The processor relays your instructions to the program in use. If necessary, it also sends commands to the iPhone's screen and other hardware. If the raw data doesn't match any applicable gestures or commands, the iPhone disregards it as an extraneous touch.

All these steps happen in a nanosecond -- you see changes in the screen based on your input almost instantly. This process allows you to access and use all of the iPhone's applications with your fingers. We'll look at these programs and the iPhone's other features, as well as how the iPhone's cost measures up to its abilities, in more detail in the next section.

The front surface of the Apple iPhone has only one button -- the Home button. Pressing the Home button takes you to the main screen of the iPhone's graphical user interface, where the pre-installed Apple applications are housed when you first get your phone. You simply swipe from right to left or vice versa to change pages and access additional apps. From any screen, you can also choose from the device's four primary functions using icons at the bottom of the screen. By default these are:

You can swap other applications into these positions by pressing and holding any one of the above until all app icons begin to shake, sliding it onto the main screen and sliding something else into the bottom area in its place.

You can open the iPhone's other applications from the upper portion of the Home screen. These include a calendar, calculator, notepad, and widgets, or mini-applications made specifically for the iPhone. Older iPhones include a 2.0- or 3.2-megapixel camera along with software you can use to organize your pictures -- the iPhone 5s model ups the stakes with an 8-megapixel camera. You can also use an iPhone to check weather reports and stock quotes. Even though the iPhone doesn't support Flash, which YouTube's non-mobile site relies on, you can watch YouTube videos using the corresponding application. An Apple version of YouTube was built in prior to iOS 6. Now the iOS requires that you download either the Google YouTube app or another video search and play app that can access YouTube. The virtual keys and buttons you need to navigate each application appear only when you need them.

The shape of the screen changes when you need it to as well -- you can shift the perspective from vertical to horizontal by tilting the phone. An accelerometer inside the iPhone lets the operating system know to change the orientation of the image on the screen. This means that you can scroll through long lists of music files on a long, narrow screen, and you can watch movies in a widescreen format. You can learn more about accelerometers in How the Wii Works.

Other physical buttons and switches, aside from the Home button, are located around the edge of the phone. An on/off or sleep button is located at the top of the phone. A switch on the left side lets you set your phone from ringing to silent, and just below that are the volume buttons.

The second generation of the iPhone introduced several new features. We'll take a closer look at those in the next section.

In June 2008, Steve Jobs unveiled the 3G iPhone at a conference for application developers. Apple offered 8 and 16 GB options of the 3G edition of the iPhone. The phone's appearance only changed a little bit -- this model has a slightly sleeker design and its back isn't silver. Customers who bought the 16 GB model could choose between an iPhone with a black or white plastic back. The 8 GB model was only available in black.

Perhaps the biggest announcement -- apart from the fact that the phone could take advantage of 3G network technology -- was that the 3G iPhone had a GPS receiver. One of the challenges of GPS devices is that they tend to drain batteries pretty quickly. That's because the device is constantly receiving signals from satellites orbiting the Earth.

Another important addition to the iPhone was support for Microsoft Exchange. Microsoft Exchange support means users can now synchronize their iPhones with their Microsoft Outlook accounts. By adding this feature, the iPhone became more competitive with other enterprise smartphones -- the phones businesses use to keep executives and employees connected when out of the office.

When it released the original iPhone, Apple didn't support third-party applications, though that didn't stop developers from writing them. But with the original iPhone, in order to even run a non-Apple application, an iPhone owner had to first jailbreak his or her phone. Jailbreaking just meant the owner could load and run third party applications. But it came with a risk -- if you tried to install official updates from Apple with a jailbroken phone, Apple could tell that some hanky panky was going on. But the 3G iPhone acts as an application platform, and Apple encourages developers to create content for it.

The transfer to the 3G iPhone didn't go without a hitch. Instead of allowing customers to purchase phones and activate them at home, Apple wanted them to activate the phones inside the store. Unfortunately, Apple's systems suffered an overload, causing massive delays during the product launch. Most customers ended up having to activate at home anyway.

Some of the new applications that became available when Apple opened up development for the iPhone take advantage of the device's accelerometer feature. Games like "Super MonkeyBall" let the player control the game character by tilting the phone in different ways. Could the iPhone become the next portable gaming platform? That's precisely what Apple claimed at its Sept. 9, 2009 press event. That brings us up to the iPhone 3GS.

Apple unveiled the iPhone 3GS at the 2009 World Wide Developers Conference (WWDC). The S stands for "speed." According to Apple, the iPhone 3GS is up to twice as fast as the previous iPhone 3G model. That applies both to accessing the data network and launching applications. In real-world tests, journalists found that the iPhone 3GS often was more effective at picking up 3G signals from the cell phone carrier than its predecessor.

But the iPhone 3GS isn't just faster than previous models. It also boasts some new features. Here's a rundown of what you'll find on the iPhone 3GS:

While these features were touted as impressive new technology, many of them already existed on other smartphones.

On the next page, we'll take a closer look at the iPhone 4.

When Steve Jobs unveiled the iPhone 4 in 2010, he confirmed a lot of rumors that had been swirling around for more than a month. The technology news blog Gizmodo made headlines of its own when it ran a story about a prototype version of the iPhone 4 ahead of the official announcement. The phone belonged to an Apple employee who apparently left it behind at a bar by accident. Gizmodo revealed many of the phone's features, though Apple had remotely locked most of its functionality.

Jobs slyly acknowledged the fact that his audience knew more about the phone than they should, but he still had some surprises up his sleeve. The new iPhone's design was a departure from previous models. Instead of the slightly curved back, the iPhone 4 has flat surfaces. It also has two cameras. The rear-facing camera takes 5-megapixel pictures and can capture 720p video. It also has an LED flash for low-light photography [source: Apple]. The front-facing camera plays a part in Apple's Facetime app, which lets you make video calls to other iPhone 4, compatible iPod touch and Mac OS X users.

The phone's front and back are both covered in glass. Metal bands around the edge of the phone act as antennae.

The iPhone 4 has what Apple calls a retina display. Its resolution is 960 by 640 pixels, or 326 pixels per inch. It has an 800-to-one contrast ratio.

Other iPhone 4 features include:

A year after the release of the iPhone 4, Apple used its annual WWDC event to announce something new -- but it wasn't a new phone. It was the next iteration of its mobile operating system, iOS, with some major improvements in tow.

Apple announced version 5.0 of its mobile operating system in June 2011, several months before it unveiled the new phone that iOS5 would launch alongside. The operating system software went through several months of beta use before becoming available for iPhones, iPads and iPod touches. The iOS 5 update is one of the biggest changes to the iPhone experience Apple has ever made. The standout new feature is Siri, the personal assistant built into iOS 5. Siri is only available on the iPhone 4S and later; the iOS 5 operating system itself can be downloaded onto the iPhone 4 and iPhone 3GS, but Siri doesn't run on those phones.

Siri uses natural language processing to interpret spoken commands. When you talk to Siri, your voice is uploaded to a server, processed, and sent back to the phone where action is taken. This only takes a couple seconds, and Siri can perform tasks like sending text messages, setting alarms, appointments and reminders, searching for restaurants, or making voice calls. By filling out contact information, Siri can understand commands like "Call my wife" or "Remind me to take my keys when I leave the office."

For all iOS 5 users, Apple revamped its notification system to be more like the convenient sliding tray found on Android. Notifications no longer pop up in the middle of the screen, interrupting an app -- they're accessible in a tray that slides down from the top of the screen with a quick swipe. Additional new features:

Steve Jobs passed away on October 5, 2011. The day before, on October 4, his chosen successor, Tim Cook, hosted the annual fall Apple event to unveil the iPhone 4S. This marked the first time Jobs didn't introduce the new iPhone, but his influence lives on in the device itself. Up until the moment the event started, there was speculation that Apple would name its new phone the iPhone 5 and that it planned to release a modified iPhone 4 as a cheap alternative called the iPhone 4S. That didn't happen. Like the iPhone 3GS, the iPhone 4S keeps the same body design as its predecessor while substantially updating its internal hardware.

The iPhone 4S introduced three major new features: faster processing with a dual-core CPU and GPU; better photography with an 8 megapixel camera; and deep voice control integration through Siri, the voice assistant software we talked about in the iOS 5 section. While iOS 5 is available as a free download for iPhone 3GS and iPhone 4 users, Siri is only accessible on the iPhone 4S and later.

Apple equipped the iPhone 4S with the same 1GHz A5 system-on-a-chip that's inside the iPad 2. The A5 chip contains dual-core CPU and GPU processing, making it dramatically faster than the A4 chip inside the iPhone 4. For processor-intensive purposes like Javascript and graphics-intensive games, the iPhone 4S outperformed all the Android devices on the market as of fall 2011. For example, in the GLBenchmark 2.1 software, the iPhone 4S could push 122 frames per second; the Samsung Galaxy S II managed 67, while the iPhone 4 managed only 15 [source: Anandtech].

The iPhone camera received a similarly big upgrade from 5 megapixels to 8 megapixels. But the image resolution isn't what makes the iPhone 4S camera so much better -- it's the new, larger sensor, which captures 73 percent more light than the one on the iPhone 4. Light sensitivity makes an enormous difference when shooting in low-light situations. Additionally, Apple employed a five-element lens system over the iPhone 4's four-element system to increase image sharpness, and improved the aperture from f/2.8 to f/2.4 to capture more light [source: Tested]. The camera can shoot 1080p video, up from the iPhone 4's 720p video shooting capabilities.

The iPhone 4S marked another significant milestone for Apple's smartphone business: The device launched simultaneously on AT&T, Sprint and Verizon in October 2011. It's the first iPhone that works on both GSM and CDMA networks, the two cellular technologies used worldwide. Dual-radio phones like the iPhone 4S are often called "worldphones." But there's a catch we'll get into on the next page: Only an unlocked iPhone 4S, sold for $650 through Apple, can use SIM cards in foreign countries.

On September 12, 2012, Apple CEO Tim Cook hosted the company's fall special event and unveiled the iPhone 5. The phone underwent a major redesign this time. Apple managed to reduce the size of many of the internal components and pack them into a tighter space. The iPhone 5 is lighter and thinner than its predecessors, but with the same width and a slightly longer body to increase the screen size. It measures 7.6 millimeters (0.30 inches) in depth, 58.6 millimeters (2.31 inches) in width, 123.8 millimeters (4.87 inches) in height, and weighs a mere 112 grams (3.95 ounces), making it 20 percent lighter than the 4S. The body is made up of anodized aluminum with ceramic glass inlays.

The new phone has a retina display with a pixel density of 326 pixels per inch just like the 4S, but the screen has increased from 3.5 inches to 4 inches (8.9 centimeters to 10.2 centimeters) diagonally, taking the resolution from 960 by 640 pixels to 1136 by 640 pixels. The new resolution makes the aspect ratio nearly 16:9, allowing you to watch widescreen HD video without letterboxing and giving more room for Web sites, e-mail and games, among other things. Some apps are already being developed to take advantage of the new screen size, while older apps will still display correctly by leaving black space on two sides. It also allows for an extra row of apps on the screen. The width was retained so that the phone would remain just as comfortable in your hand as previous phones.

The screen now has the touch sensors integrated with the display, meaning there is one layer with the pixels acting as touch-sensing electrodes, rather than a display layer and a separate capacitive touch sensing layer laid over it. Behind the scenes, there are now two chips controlling the touchscreen rather than one, but despite these differences, multi-touch functionality remains the same. Removing the extra layer makes the phone thinner, and also reduces glare and makes images sharper.

The iPhone 5 includes a new processor called the A6, the first one designed entirely in-house by Apple. Both the CPU and graphics speeds are faster than those of the A5, and it is touted to perform most tasks nearly twice as fast as its predecessor, while keeping battery usage about the same or even slightly lower by working efficiently with the new iOS 6 operating system (to be discussed in the next section). This means faster app loading, faster photo capture, quicker Internet surfing and better gameplay.

The new phone supports more cellular networks than the previous models, adding HSPA+, DC-HSDPA and the new ultra-fast LTE wireless technology (up to 100 megabits per second download) to the mix. A new single voice and data chip and a dynamic antenna can switch connections between different networks. The iPhone 5 works with more WiFi standards than previous versions -- WiFi is now 802.11 a/b/g/n rather than just b/g/n, and its 802.11n is both 2.4 GHz and dual-channel 5GHz with download speeds of up to 150 megabits per second, although this, like the 100 MBPS of LTE, is a theoretical maximum [source: Cook].

The iSight rear-facing camera and FaceTime front-facing cameras both underwent improvements. The iSight's lens is now made of sapphire crystal, nearly as hard as diamond and more difficult to scratch. Lens alignment was made more precise, and a new dynamic low-light mode makes it work better in dim situations. The FaceTime's video quality has been upgraded to 720p high-definition, and it now has backside illumination. The iPhone 5 also has three microphones, located on the bottom, front and back of the phone. They allow for noise cancellation and beamforming, techniques that improve audio quality.

The traditional 30-pin connector has been replaced with Apple's Lighting connector, which is 80 percent smaller. The bad news is that many existing accessories are only compatible with the 30-pin connector. The good news is that there is a Lightning-to-30-pin adapter available for purchase, and that the new connector is reversible, meaning no more instances of trying to insert the connector the wrong way and having to flip it over.

The device also comes with new redesigned EarPods rather than the traditional EarBuds. The EarPods reportedly provide higher-quality sound and fit more comfortably into a wider variety of ear shapes than their predecessors EarBuds.

About 5 million units of the iPhone 5 were sold during the first weekend of availability, breaking the sales records of the iPhone 4s [sources: Satariano, Martin].

Read on to find out about the new version of iOS unveiled alongside the iPhone 5.

On Sept. 10, 2013, Apple announced new versions of its iPhone 5, named the iPhone 5s and 5c. The former is an all-new phone, featuring updated hardware and capabilities, while the latter is a minor update on the older iPhone 5.

The 5c is intended as a budget-friendly device, and with a two-year contract the 16GB version sold for $99 when it premiered in the U.S. The 32GB model sold for $100 more. One of the phone's key marketing points is color -- instead of a metal case, consumers can choose from a plastic exterior that comes in five different hues. Although the colors may be different, the guts of the phone are still the same as the iPhone 5.

However, the 5c's battery and antennas are different than the iPhone 5. The battery has a higher capacity, and thus will store a longer-lasting charge. Apple says that the antennas will support more frequencies worldwide than any other smartphone.

In terms of media hype, most focus went directly to the iPhone 5s, which features significant hardware changes.

Apple overhauled the iconic home button by adding an integrated fingerprint sensor. After registering a fingerprint with the device, a simple fingertip press unlocks the phone, authorizes online purchases and completes other actions that require heightened security.

This capability is called TouchID. The sensor can read sub-surface skin layers at a resolution of 500 pixels per inch and at any angle. You can register more than one person on the phone so that multiple people can access secure functions. Although hailed as a step forward in user-friendly security, the feature was defeated by a computer club just a few days following the phone's release [source: Diaz].

Instead of the A6 chip, the 5s sports a new A7 processor, which is the first 64-bit processor ever built into a smartphone. When running apps optimized for 64-bit functionality, the processor should result in faster and more efficient performance.

Apple built in a secondary processor called the M7, which is dedicated to handling signals from the phone's built-in accelerometer and gyroscopes. The M7 chip should shoulder some of the processing load that would otherwise go to the primary A7 chip.

The phone's camera is, like its predecessor, 8 megapixels, but it has some new tricks. Instead of one LED flash, it features two, in white and amber. The idea is that the phone will automatically choose the best flash depending on ambient light, which results in better color balance and improved picture quality. The camera also has a wider aperture (at f/2.2), slow motion video, 10 frames per second burst mode and image stabilization.

Hardware aside, both the 5c and 5s run iOS 7, which is Apple's newest mobile operating system. On the next page you'll read all about iOS's new features.

A few advance reviewers bashed the latest iPhones as rather stale in terms of hardware. However, iOS 7 includes whole lot of major changes for Apple devotees to process.

First and foremost, the overall visual interface is quite different from older versions of iOS. It's considered the biggest overhaul for the operating system since 2007. In iOS 7, gone are the frilly graphical flourishes, such as faux leather for the calendar app and wood for the Newsstand app, replaced by a simpler, stripped-down appearance. There are new icons and fonts, transparency effects, and advanced graphics physics designed to make the display look more three dimensional.

The so-called live wallpapers are on prominent display in this iOS. These wallpapers feature on-screen bubbles that float about in different directions depending the phone's orientation.

Beyond the eye candy, there are plenty of changes in the way iOS actually works, too. One of the most notable updates is Control Center access. Just swipe up anywhere and you'll have immediate access to wireless options, screen brightness, flashlight, airplane mode and music controls.

The burgeoning App Store, which is at around 900,000 apps and counting, has improved search capabilities. You can filter apps by their popularity in your geographical location, and you can filter them by age appropriateness, too, which should please some parents. Apps can now update automatically in the background instead of requiring your manual intervention.

iOS 7 integrates with iTunes and a range of cloud-based capabilities. Instead of playing only tracks stored to the device itself, you can access music stored in iCloud. There's also the long-overdue ability to build Pandora-like radio stations around specific artists and songs.

Apple's Web browser, Safari, now has a combined URL and search text box. That simply means you can either directly type the Web site you want to access or instead initiate an Internet search. Phones from other companies have been doing this for some time, but this is a first for iOS. Safari also now lets you open just about as many tabs as you want, and then swipe them away once you're done with those pages.

Voice-command app Siri has some new tricks, as well. Simply say "increase screen brightness" or "turn on WiFi," and Siri immediately does so. You can choose new voices and languages for Siri, too.

The version of iOS is also slated for all kind of in-vehicle integration. In 2014, about a dozen car makers will offer displays that communicate directly with the iPhone. Simply speak a command and the car will read back messages to you (and let you speak replies), let you control the music system, and of course, control mapping capabilities.

AirDrop is now integrated into the OS. With AirDrop, you can use your iPhone to share files with other Apple products through a WiFi signal.

The Camera app allows live previews of various creative filters. You can also swipe between various frame shapes (such as panoramic or square).

There are dozens of other minor tweaks to iOS, all designed to make a complicated device easy to use. Later, you'll see how Apple's newest iPhone stacks up against the competition.

The iPhone 4S set records as Apple's fastest-selling phone -- the company moved more than 4 million units in the device's first weekend on the market [source: CNET]. And the iPhone 5 beat that record by selling around 5 million units on its debut weekend.

The iPhone 5c and 5s, however, took Apple to even greater heights. After only three days of sales, around 9 million of these new phones had been sold, making these iterations of the iPhone the most popular by far, and providing the company with a riposte to critics who say post-Steve Jobs Apple is losing its innovative edge. Many of the new sales were attributed to the fact that for the first time, China's market was included in the iPhone's rollout [Source: Reuters].

The iPhone has gotten a lot of attention in the press, but other phone models already have similar features. As of late 2013, phones running Android, the mobile operating system designed by Google, were leading the smartphone OS arena at nearly 80 percent versus Apple's 17 percent [source: Fox News].

However, the Android share is spread out over many devices and manufacturers. Apple reaps all the rewards from iPhone sales. What's more, Apple's strategy has always been to maximize profit margin and not market share.

The iPhone changed the face of the phone market as we know it. While "smartphones" existed before the iPhone, Apple's focus on touch controls pushed the industry in a new direction. The once-common Windows Phone 6.x line was phased out in favor of an entirely new operating system with Windows Phone 7. RIM's BlackBerry line has been in decline for years. Android has given Apple its most serious competition with an open source OS embraced by a range of electronics companies.

Apple launched its first CDMA iPhone to U.S. users in early 2011, when it made the iPhone 4 available on Verizon's cellular network. With the iPhone 4S, the company released one model using a dual-mode chipset to work on Sprint and Verizon's CDMA networks and AT&T's GSM network. That means the phone can roam in other countries on either kind of network. Ideally, it would also mean foreign SIMs (subscriber identity modules) could be loaded into the phone to pay local rates while traveling abroad in GSM countries. But that's not how it works: The iPhone 4S comes locked to a specific network. To use it abroad, there are two choices: Buy an unlocked model directly from Apple (at a premium), or pay a cellular carrier for a global roaming plan.

With the flagship iPhone 5s, Apple released four models: the A1533, A1453, A1457 and A1530, along with four versions of the 5c. All four configurations support different radio bands, and Apple packs as many as possible in each version so that it has fewer different models to produce and manage.

No single carrier offers a clear-cut best option as of fall 2013. Sprint offers an unlimited data plan, Verizon now only offers limited data share plans that allow customers to share a set amount of data over multiple devices, and AT&T also forces new customers into similar limited data mobile share plans, but allows older iPhone customers to be grandfathered into the unlimited plan, provided they come into a retail store and request this option, and do not order online.

Carrier voice plans for the iPhone also vary in price and available minutes. Verizon and AT&T are both larger networks that may provide better cellular coverage, depending on your region. Sprint and Verizon's CDMA technology cannot use voice and data simultaneously, and the latest iPhone supports faster HSPA+ (also known as Evolved High-Speed Packet Access)data on AT&T's GSM network. In real-world use, data speeds vary by network usage and location -- Verizon or Sprint could potentially be faster than AT&T based on those factors. All carrier services are also developing much faster LTE networks, but those are only available in certain areas, and only the iPhone 5 can take advantage of LTE. You have to weigh a variety of factors and pick the best carrier, plan and phone for you.