How Semiconductors Work

Semiconductors have had a monumental impact on our society. You find semiconductors at the heart of microprocessor chips as well as transistors. Anything that's computerized or uses radio waves depends on semiconductors.

Today, most semiconductor chips and transistors are created with silicon. You may have heard expressions like "Silicon Valley" and the "silicon economy," and that's why -- silicon is the heart of any electronic device.

A diode is the simplest possible semiconductor device, and is therefore an excellent beginning point if you want to understand how semiconductors work. In this article, you'll learn what a semiconductor is, how doping works and how a diode can be created using semiconductors. But first, let's take a close look at silicon.

Silicon is a very common element -- for example, it is the main element in sand and quartz. If you look "silicon" up in the periodic table, you will find that it sits next to aluminum, below carbon and above germanium.

Silicon sits next to aluminum and below carbon in the periodic table.

Carbon, silicon and germanium (germanium, like silicon, is also a semiconductor) have a unique property in their electron structure -- each has four electrons in its outer orbital. This allows them to form nice crystals. The four electrons form perfect covalent bonds with four neighboring atoms, creating a lattice. In carbon, we know the crystalline form as diamond. In silicon, the crystalline form is a silvery, metallic-looking substance.

In a silicon lattice, all silicon atoms bond perfectly to four neighbors, leaving no free electrons to conduct electric current. This makes a silicon crystal an insulator rather than a conductor.

­ Metals tend to be good conductors of electricity because they usually have "free electrons" that can move easily between atoms, and electricity involves the flow of electrons. While silicon crystals look metallic, they are not, in fact, metals. All of the outer electrons in a silicon crystal are involved in perfect covalent bonds, so they can't move around. A pure silicon crystal is nearly an insulator -- very little electricity will flow through it.

But you can change all this through a process called doping.

Doping Silicon

You can change the behavior of silicon and turn it into a conductor by doping it. In doping, you mix a small amount of an impurity into the silicon crystal.

There are two types of impurities:

• N-type - In N-type doping, phosphorus or arsenic is added to the silicon in small quantities. Phosphorus and arsenic each have five outer electrons, so they're out of place when they get into the silicon lattice. The fifth electron has nothing to bond to, so it's free to move around. It takes only a very small quantity of the impurity to create enough free electrons to allow an electric current to flow through the silicon. N-type silicon is a good conductor. Electrons have a negative charge, hence the name N-type.
• P-type - In P-type doping, boron or gallium is the dopant. Boron and gallium each have only three outer electrons. When mixed into the silicon lattice, they form "holes" in the lattice where a silicon electron has nothing to bond to. The absence of an electron creates the effect of a positive charge, hence the name P-type. Holes can conduct current. A hole happily accepts an electron from a neighbor, moving the hole over a space. P-type silicon is a good conductor.

A minute amount of either N-type or P-type doping turns a silicon crystal from a good insulator into a viable (but not great) conductor -- hence the name "semiconductor."

N-type and P-type silicon are not that amazing by themselves; but when you put them together, you get some very interesting behavior at the junction. That's what happens in a diode.

A diode is the simplest possible semiconductor device. A diode allows current to flow in one direction but not the other. You may have seen turnstiles at a stadium or a subway station that let people go through in only one direction. A diode is a one-way turnstile for electrons.

When you put N-type and P-type silicon together as shown in this diagram, you get a very interesting phenomenon that gives a diode its unique properties.

Even though N-type silicon by itself is a conductor, and P-type silicon by itself is also a conductor, the combination shown in the diagram does not conduct any electricity. The negative electrons in the N-type silicon get attracted to the positive terminal of the battery. The positive holes in the P-type silicon get attracted to the negative terminal of the battery. No current flows across the junction because the holes and the electrons are each moving in the wrong direction.

If you flip the battery around, the diode conducts electricity just fine. The free electrons in the N-type silicon are repelled by the negative terminal of the battery. The holes in the P-type silicon are repelled by the positive terminal. At the junction between the N-type and P-type silicon, holes and free electrons meet. The electrons fill the holes. Those holes and free electrons cease to exist, and new holes and electrons spring up to take their place. The effect is that current flows through the junction.

Diodes and Transistors

A device that blocks current in one direction while letting current flow in another direction is called a diode. Diodes can be used in a number of ways. For example, a device that uses batteries often contains a diode that protects the device if you insert the batteries backward. The diode simply blocks any current from leaving the battery if it is reversed -- this protects the sensitive electronics in the device.
A semiconductor diode's behavior is not perfect, as shown in this graph:

When reverse-biased, an ideal diode would block all current. A real diode lets perhaps 10 microamps through -- not a lot, but still not perfect. And if you apply enough reverse voltage (V), the junction breaks down and lets current through. Usually, the breakdown voltage is a lot more voltage than the circuit will ever see, so it is irrelevant.
When forward-biased, there is a small amount of voltage necessary to get the diode going. In silicon, this voltage is about 0.7 volts. This voltage is needed to start the hole-electron combination process at the junction.
Another monumental technology that's related to the diode is the transistor. Transistors and diodes have a lot in common.

Transistors

A transistor is created by using three layers rather than the two layers used in a diode. You can create either an NPN or a PNP sandwich. A transistor can act as a switch or an amplifier.
A transistor looks like two diodes back-to-back. You'd imagine that no current could flow through a transistor because back-to-back diodes would block current both ways. And this is true. However, when you apply a small current to the center layer of the sandwich, a much larger current can flow through the sandwich as a whole. This gives a transistor its switching behavior. A small current can turn a larger current on and off.
A silicon chip is a piece of silicon that can hold thousands of transistors. With transistors acting as switches, you can create Boolean gates, and with Boolean gates you can create microprocessor chips.
The natural progression from silicon to doped silicon to transistors to chips is what has made microprocessors and other electronic devices so inexpensive and ubiquitous in today's society. The fundamental principles are surprisingly simple. The miracle is the constant refinement of those principles to the point where, today, tens of millions of transistors can be inexpensively formed onto a single chip.

Wonderful word

Alexander’s Last Words:-

   “Burn my Body & Keep my hands outside, because the world should know, the man won the World. Had Nothing in his hands”.

Adjustment is always better than Argument. A meaningful silence is better than the meaningless words.

True guidance is like a small lamp in a dark forest. It doesn’t show everything at once, but gives enough light for the next step to be safe.

When you collect all the answers of life, God just changes the question paper. That’s life.

All fools can tell the ‘truth’ easily. But Only the Intelligent can tell the ‘Suitable Lie’

Heavenly Truth: - “The most painful moment life comes. When the care is mistaken as disturbance.

 Every one acts as like a fresher in their own problems. But, In case of others problems, everyone acts an Experts.

What is Richness?

 True Answer by Swami Vivekananda:-

 “Richness is not earning more, spending more or saving more.  Richness is when you need ”No More”

Understanding human nature is the highest knowledge, and only by knowing it can we know God. It is also a fact that the knowledge of God is the highest knowledge, and only by knowing God can we understand human nature.

 

Opinions are like Hand Watches. Everyone’s watch shows different time from others. But, everyone believes that their time is correct. That’s life.

Amazing truth:

”Poor people beg outside the temple and Rich people beg inside the Temple” – Periyar.

Unbeatable lines:-

 “The Pain you feel today. It will be the strength of tomorrow".

“Think Positive., It shows a correct way.

  Think Negative., It shows a safe way” – Hilter.

3 simple steps to play safe in the game of life

Don’t promise when you are happy!

Don’t reply when you are angry!

Don’t decide when you are sad! .

Think before you speak.

T- Is it True/

H- Is it Help?

I-  Is it Inspiring?

N- Is it Necessary?

K -Is it Kind?

So think twice and act Wise.

Life is not a sharp knife to cut all the bad memories. But life is a Needle to weave Golden Thread of sweet Memories.

Minds are like pens they work only when open

All our efforts cannot be translated into success. But they can act as a foundation stone for a glorious future

This moment is not permanent in life.

Read above line whenever you are happy and sad.

Three things in life that, once gone, never come back.

1. Time

2. Words

3. Opportunity

Wonderful word by  Dr.A.P.J Abdul Kalam.

  “Don’t dream about beauty... It spoils your duty.  Dream about your duty… it makes your life beauty!!!!”

One Best book is equal to hundred good Friends.

But one good friend is equal to A Library.

Forget injuries,but never forget Kindness.

Never cry for the person who hurts you..just Smile and say: Thanks for giving me a chance to find someone better than you.

How the iPhone Works

On January 2007, Steve Jobs introduced the Apple iPhone during his keynote address at the Macworld Conference and Expo. In its first appearance onscreen and in Jobs's hand, the phone looked like a sleek but inanimate black rectangle.

Then, Jobs touched the screen. Suddenly, the featureless rectangle became an interactive surface. Jobs placed a fingertip on an on-screen arrow and slid it from left to right. When his finger moved, the arrow moved with it, unlocking the phone. To some people, this interaction between a human finger and an on-screen image -- and its effect on the iPhone's behavior -- was more amazing than all of its other features combined.

And those features are plentiful. In some ways, the iPhone is more like a palmtop computer than a cellular phone. As with many smartphones, you can use it to make and receive calls, watch movies, listen to music, browse the Web, and send and receive e-mail and text messages. You can also take pictures and video (using an iPhone 3GS or later model) with a built-in camera, import photos from your computer and organize them all using the iPhone's software.

In 2008, Apple introduced the second generation iPhone. This iPhone can operate on third-generation (3G) cellular networks and has a GPS receiver. It also lets you view map and satellite data from Google Maps, including overlays of nearby businesses. Owners of the original iPhone got the opportunity to upgrade the software on their phones. The 2.0 software gives the old phones new functions, but without the GPS receiver or 3G network capability.

2009 was the year that Apple launched the iPhone 3GS. The 3GS iPhone models have more storage capacity than earlier iPhones. They also have a better camera that's capable of taking still shots and video at 30 frames per second. Another added feature is a compass, which comes in handy when you need to find your way through unfamiliar territory. Also in 2009 came iPhone OS 3.0, which offered many improvements, such as the ability to cut and paste.

In 2010, Steve Jobs took the stage to announce a new generation of Apple's runaway success: the iPhone 4. The new device sports two cameras -- one on the front and one on the back. The iPhone 4 has a retina display with a better resolution than earlier phones. It also marked a departure from the basic iPhone design -- the phone doesn't have a slightly curved back so it lays flat on surfaces. Jobs also announced a new name for the iPhone operating system: iOS.

A modified version of the Macintosh OS X operating system used on Apple desktop and laptop computers lets you interact with all of these applications. It displays icons for each application on the iPhone's screen. It also manages battery power and system security. The operating system synchs the phone with your computer, a process that requires a dock much like the one used to synch an iPod. It also lets you multitask and move through multiple open applications, just like you can on a laptop or desktop computer
.

But instead of using a mouse or a physical keyboard, the iPhone uses virtual buttons and controls that appear on its screen. This isn't really a new phenomenon -- touch screens have been part of everything from self-checkout kiosks to smartphones for years. But the iPhone's touch screen is a little different from many of the others currently on the market. When you touch the screen on a PDA or a Nintendo DS, you typically use a slender, pointed stylus. The iPhone, on the other hand, requires you to use your fingers. It can also detect multiple touch points simultaneously, which many existing touch screens cannot do.

iPhone Touch Screen

The conductive layers in the iPhone's touch screen enable users to give the device commands with a simple swipe of the finger.

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 pagesor 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.

Multi-touch Systems

The many component layers in a mutual capacitance screen.

To allow people to use touch commands that require multiple fingers, the iPhone uses a new 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.

Unlike the mutual capacitance circuitry, a self capacitance screen contains a transparent electrode layer.

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.

iPhone Processor

The iPhone's touch screen registers your touch and converts that raw data into precise coordinates.

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.

Phone Features

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. There, you can choose from the device's four primary functions using icons at the bottom of the phone:

• Phone: 3G, GSM or EDGE cellular phone service as well as a visual voice mail menu
• Mail: POP and IMAP e-mail access, including in-line pictures, HTML capabilities and push e-mail
• Web: Safari Web browser
• iPod: Music and videos

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 and software you can use to organize your pictures -- the iPhone 4 ups the stakes with a 5-megapixel camera. You can also use an iPhone to check weather reports and stock quotes. Even though the iPhone doesn't support Flash, which the YouTube site relies on, you can watch YouTube videos using the corresponding application. The 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. 

3G iPhone Applications and Problems

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 had 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 means 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.

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:

• More storage space: There are two versions of the iPhone 3GS: 16 GB and 32 GB models. This doubles the capacity of older iPhone models. Both models are available in white or black.
• Video camera: Not only does the iPhone 3GS's camera capture larger photos (3.2 megapixels versus the iPhone 3G's 2.0 megapixel camera), it can record video at 30 frames per second, too. The camera can focus automatically or you can use the touch screen to tell the camera where to focus the image. It also adjusts the image's white balance automatically.
• Voice control: While many other phones on the market have voice dialing features, the iPhone 3GS's voice control extends the functionality to other parts of the phone. Not only can you make calls by speaking into your phone, you can also control music playback and other functions.
• Compass: When paired with the accelerometer and GPS receiver, the iPhone 3GS's compass helps keep iPhone owners from getting lost. It also allows app developers the opportunity to develop augmented reality applications.
• Oleophobic screen: One problem with touch screens is that they tend to attract smudges. The iPhone 3GS has an oleophobic screen. An oleophobic material repels oils, keeping the screen relatively smudge-free.
• Tethering: If your cell phone carrier allows it, you can use the iPhone 3GS as a modem for your computer. Simply hook the iPhone 3GS to the computer using an Apple USB cord and you can surf the Web at 3G speeds. Some carriers don't allow tethering, including AT&T in the United States.

In the nanosecond between the time you touch the iPhone's screen and the display reacts, several calculations and signals are sent from the touch screen to the software.

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.

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 appeared to leave 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. Another big departure from previous iPhone models are the buttons: The iPhone 4 has four buttons or switches around the edge of the phone. One is the on/off switch, the second controls volume and the third lets you switch your phone from ringing to silent. The fourth button is the Home button.

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:

• multitasking
• HD video recording and editing
• camera autofocus
• three-axis gyroscope
• dual-mic noise suppression

iOS 5

Apple announced version 5.0 of its mobile operating system in June 2011, several months before it unveiled the new phone 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 updater is one of the biggest updates 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; 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."

iPhone 4 and 3GS users still have new features to look forward to as well. 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:

• Apple's iMessage service integrates various communication sources like text messages and iChat. If you're sending a SMS to another iPhone owner, iOS5 defaults to iMessage, saving you a text.
• New iPhones can be activated without connecting to a computer, and data can be synced from iTunes over WiFi.
• The iCloud service syncs up to 5GB of apps, photos, and documents across multiple Apple devices for free.
• Twitter is built into the OS.
• The camera can be accessed from the lock screen.
• Light photo editing like red eye removal and cropping can be done from the Photos app.
• Apple's AirPlay video streaming works wirelessly. Video can be wirelessly mirrored from an iPad 2 or iPhone 4S to an Apple TV.
• Apple added new multi-touch gestures for multitasking.

iPhone 4S

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.

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 outperforms 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

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, that Apple picked. 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 . The camera can shoot 1080p video, up from the iPhone 4's 720p video shooting capabilities.

The iPhone 4S marks 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."