Imagine you're James Bond, and you have to get into a secret laboratory to disarm a deadly biological weapon and save the world. But first, you have to get past the security system. It requires more than just a key or a password -- you need to have the villain's irises, his voice and the shape of his hand to get inside. You might also encounter this scenario, minus the deadly biological weapon, during an average day on the job. Airports, hospitals, hotels, grocery stores and even Disney theme parks increasingly use biometrics -- technology that identifies you based on your physical or behavioral traits -- for added security.
In this article, you'll learn about biometric systems that use handwriting, hand geometry, voiceprints, iris structure and vein structure. You'll also learn why more businesses and governments use the technology and whether Q's fake contact lenses, recorded voice and silicone hand could really get James Bond into the lab (and let him save the world).
You take basic security precautions every day -- you use a key to get into your house and log on to your computer with a username and password. You've probably also experienced the panic that comes with misplaced keys and forgotten passwords. It isn't just that you can't get what you need -- if you lose your keys or jot your password on a piece of paper, someone else can find them and use them as though they were you.
Biometrics vs. Forensics
Biometrics and forensics have a lot in common, but they're not exactly the same. Biometrics uses your physical or behavioral characteristics to determine your identity or to confirm that you are who you claim to be. Forensics uses the same kind of information to establish facts in civil or criminal investigations.
Instead of using something you have (like a key) or something you know (like a password), biometrics uses who you are to identify you. Biometrics can use physical characteristics, like your face, fingerprints, irises or veins, or behavioral characteristics like your voice, handwriting or typing rhythm. Unlike keys and passwords, your personal traits are extremely difficult to lose or forget. They can also be very difficult to copy. For this reason, many people consider them to be safer and more secure than keys or passwords.
Biometrics uses unique features, like the iris of your eye, to identify you.
Biometric systems can seem complicated, but they all use the same three steps:
Enrollment: The first time you use a biometric system, it records basic information about you, like your name or an identification number. It then captures an image or recording of your specific trait.
Storage: Contrary to what you may see in movies, most systems don't store the complete image or recording. They instead analyze your trait and translate it into a code or graph. Some systems also record this data onto a smart card that you carry with you.
Comparison: The next time you use the system, it compares the trait you present to the information on file. Then, it either accepts or rejects that you are who you claim to be.
Systems also use the same three components:
A sensor that detects the characteristic being used for identification
A computer that reads and stores the information
Software that analyzes the characteristic, translates it into a graph or code and performs the actual comparisons
Biometric security systems, like the fingerprint scanner available on the IBM ThinkPad T43 (right), is becoming more common for home use. You can read other articles to learn about face recognition and fingerprint scanning. Next, we'll examine how biometrics provides security using other traits, starting with handwriting.
Pictures & Codes
Movies and television shows often depict the process of comparing traits in a way that is fun to watch, but not accurate. For example, you may see a whole fingerprint compared to other whole fingerprints until a computer finds a match. This method would be slow and difficult. Instead of comparing actual pictures, biometric systems use various algorithms to analyze and encode information about the trait. This information takes up only a few bits of space.
Handwriting
At first glance, using handwriting to identify people might not seem like a good idea. After all, many people can learn to copy other people's handwriting with a little time and practice. It seems like it would be easy to get a copy of someone's signature or the required password and learn to forge it. But biometric systems don't just look at how you shape each letter; they analyze the act of writing. They examine the pressure you use and the speed and rhythm with which you write. They also record the sequence in which you form letters, like whether you add dots and crosses as you go or after you finish the word.
This Tablet PC has a signature verification system.
Unlike the simple shapes of the letters, these traits are very difficult to forge. Even if someone else got a copy of your signature and traced it, the system probably wouldn't accept their forgery. A handwriting recognition system's sensors can include a touch-sensitive writing surface or a pen that contains sensors that detect angle, pressure and direction. The software translates the handwriting into a graph and recognizes the small changes in a person's handwriting from day to day and over time.
Determining Accuracy
All biometric systems use human traits that are, to some degree, unique. Which system is best depends on the necessary level of security, the population who will use the system and the system's accuracy. Most manufacturers use measurements like these to describe accuracy:
False Accept Rate (FAR): How many imposters the system accepts
False Reject Rate (FRR): How many authorized users the system rejects
Failure to Enroll Rate (FTE): How many people's traits are of insufficient quality for the system to use
Failure to Acquire Rate (FTA): How many times a user must present the trait before the system correctly accepts or rejects them
Hand and Finger Geometry
A hand geometry scanner
People's hands and fingers are unique -- but not as unique as other traits, like fingerprints or irises. That's why businesses and schools, rather than high-security facilities, typically use hand and finger geometry readers to authenticate users, not to identify them. Disney theme parks, for example, use finger geometry readers to grant ticket holders admittance to different parts of the park. Some businesses use hand geometry readers in place of timecards. Systems that measure hand and finger geometry use a digital camera and light. To use one, you simply place your hand on a flat surface, aligning your fingers against several pegs to ensure an accurate reading. Then, a camera takes one or more pictures of your hand and the shadow it casts. It uses this information to determine the length, width, thickness and curvature of your hand or fingers. It translates that information into a numerical template. Hand and finger geometry systems have a few strengths and weaknesses. Since hands and fingers are less distinctive than fingerprints or irises, some people are less likely to feel that the system invades their privacy. However, many people's hands change over time due to injury, changes in weight or arthritis. Some systems update the data to reflect minor changes from day to day. For higher-security applications, biometric systems use more unique characteristics, like voices. We'll look at those next.
Authenticate vs. Identify
A biometric system can either authenticate that you are who you say you are, or it can identify you by comparing your information to all of the information on file. Authentication is a one-to-one comparison; it compares your characteristic with your stored information. Identification, on the other hand, is a one-to-many comparison.
Voiceprints
Your voice is unique because of the shape of your vocal cavities and the way you move your mouth when you speak. To enroll in a voiceprint system, you either say the exact words or phrases that it requires, or you give an extended sample of your speech so that the computer can identify you no matter which words you say. When people think of voiceprints, they often think of the wave pattern they would see on an oscilloscope. But the data used in a voiceprint is a sound spectrogram, not a wave form. A spectrogram is basically a graph that shows a sound's frequency on the vertical axis and time on the horizontal axis. Different speech sounds create different shapes within the graph. Spectrograms also use colors or shades of grey to represent the acoustical qualities of sound. This tutorial has a lot more information on spectrograms and how to read them.
Speaker recognition systems use spectrograms to represent human voices.
Some companies use voiceprint recognition so that people can gain access to information or give authorization without being physically present. Instead of stepping up to an iris scanner or hand geometry reader, someone can give authorization by making a phone call. Unfortunately, people can bypass some systems, particularly those that work by phone, with a simple recording of an authorized person's password. That's why some systems use several randomly-chosen voice passwords or use general voiceprints instead of prints for specific words. Others use technology that detects the artifacts created in recording and playback. Other systems are more difficult to bypass. We'll look at some of those next.
Layered vs. Multimodal
For some security systems, one method of identification is not enough. Layered systems combine a biometric method with a keycard or PIN. Multimodal systems combine multiple biometric methods, like an iris scanner and a voiceprint system.
Iris Scanning
Iris scanning can seem very futuristic, but at the heart of the system is a simple CCD digital camera. It uses both visible and near-infrared light to take a clear, high-contrast picture of a person's iris. With near-infrared light, a person's pupil is very black, making it easy for the computer to isolate the pupil and iris.
Eye anatomy
When you look into an iris scanner, either the camera focuses automatically or you use a mirror or audible feedback from the system to make sure that you are positioned correctly. Usually, your eye is 3 to 10 inches from the camera. When the camera takes a picture, the computer locates:
The center of the pupil
The edge of the pupil
The edge of the iris
The eyelids and eyelashes
It then analyzes the patterns in the iris and translates them into a code.
An iris scanner
Iris scanners are becoming more common in high-security applications because people's eyes are so unique (the chance of mistaking one iris code for another is 1 in 10 to the 78th power [ref]. They also allow more than 200 points of reference for comparison, as opposed to 60 or 70 points in fingerprints. The iris is a visible but protected structure, and it does not usually change over time, making it ideal for biometric identification. Most of the time, people's eyes also remain unchanged after eye surgery, and blind people can use iris scanners as long as their eyes have irises. Eyeglasses and contact lenses typically do not interfere or cause inaccurate readings.
Retinal Scans
Some people confuse iris scans with retinal scans. Retinal scans, however, are an older technology that required a bright light to illuminate a person's retina. The sensor would then take a picture of the blood vessel structure in the back of the person's eye. Some people found retinal scans to be uncomfortable and invasive. People's retinas also change as they age, which could lead to inaccurate readings.
Vein Geometry
As with irises and fingerprints, a person's veins are completely unique. Twins don't have identical veins, and a person's veins differ between their left and right sides. Many veins are not visible through the skin, making them extremely difficult to counterfeit or tamper with. Their shape also changes very little as a person ages.
Vein scanners use near-infrared light to reveal the patterns in a person’s veins.
To use a vein recognition system, you simply place your finger, wrist, palm or the back of your hand on or near the scanner. A camera takes a digital picture using near-infrared light. The hemoglobin in your blood absorbs the light, so veins appear black in the picture. As with all the other biometric types, the software creates a reference template based on the shape and location of the vein structure. Scanners that analyze vein geometry are completely different from vein scanning tests that happen in hospitals. Vein scans for medical purposes usually use radioactive particles. Biometric security scans, however, just use light that is similar to the light that comes from a remote control. NASA has lots more information on taking pictures with infrared light. Next, we'll look at some of the concerns about biometric methods.
The Future of Biometrics
Biometrics can do a lot more than just determine whether someone has access to walk through a particular door. Some hospitals use biometric systems to make sure mothers take home the right newborns. Experts have also advised people to scan their vital documents, like birth certificates and social security cards, and store them in biometrically-secured flash memory in the event of a national emergency. Here are some biometric technologies you might see in the future:
New methods that use DNA, nail bed structure, teeth, ear shapes, body odor, skin patterns and blood pulses
More accurate home-use systems
Opt-in club memberships, frequent buyer programs and rapid checkout systems with biometric security
More prevalent biometric systems in place of passports at border crossings and airports
Privacy and Other Concerns
Some people object to biometrics for cultural or religious reasons. Others imagine a world in which cameras identify and track them as they walk down the street, following their activities and buying patterns without their consent. They wonder whether companies will sell biometric data the way they sell e-mail addresses and phone numbers. People may also wonder whether a huge database will exist somewhere that contains vital information about everyone in the world, and whether that information would be safe there. At this point, however, biometric systems don't have the capability to store and catalog information about everyone in the world. Most store a minimal amount of information about a relatively small number of users. They don't generally store a recording or real-life representation of a person's traits -- they convert the data into a code. Most systems also work in only in the one specific place where they're located, like an office building or hospital. The information in one system isn't necessarily compatible with others, although several organizations are trying to standardize biometric data. In addition to the potential for invasions of privacy, critics raise several concerns about biometrics, such as:
Over reliance: The perception that biometric systems are foolproof might lead people to forget about daily, common-sense security practices and to protect the system's data.
Accessibility: Some systems can't be adapted for certain populations, like elderly people or people with disabilities.
Interoperability: In emergency situations, agencies using different systems may need to share data, and delays can result if the systems can't communicate with each other.
As Seen on TV
Television shows and movies can make it look spectacularly easy or spectacularly difficult to get past biometric security. They usually show people trying to get past the sensors rather than replacing the data in the system with their own or "piggybacking" their way in by following someone with authorization. Here are some of the more common tricks and whether they're likely to work.
Although small in size, the eye is a very complex organ.
It's no accident that the main function of the sun at the center of our solar system is to provide light. Light is what drives life. It's hard to imagine our world and life without it. The sensing of light by living things is almost universal. Plants use light through photosynthesis to grow. Animals use light to hunt their prey or to sense and escape from predators.
Some say that it is the development of stereoscopic vision, along with the development of the large human brain and the freeing of hands from locomotion, that have allowed humans to evolve to such a high level.
In this article, we'll discuss the amazing inner workings of the human eye!
Basic Anatomy
Although small in size, the eye is a very complex organ. The eye is approximately 1 inch (2.54 cm) wide, 1 inch deep and 0.9 inches (2.3 cm) tall.
The eye is unique in that it is able to move in many directions to maximize the field of vision.
The tough, outermost layer of the eye is called the sclera. It maintains the shape of the eye. The front sixth of this layer is clear and is called the cornea. All light must first pass through the cornea when it enters the eye. Attached to the sclera are the muscles that move the eye, called the extraocular muscles. The choroid (or uveal tract) is the second layer of the eye. It contains the blood vessels that supply blood to structures of the eye. The front part of the choroid contains two structures:
The ciliary body - The ciliary body is a muscular area that is attached to the lens. It contracts and relaxes to control the size of the lens for focusing.
The iris - The iris is the colored part of the eye. The color of the iris is determined by the color of the connective tissue and pigment cells. Less pigment makes the eyes blue; more pigment makes the eyes brown. The iris is an adjustable diaphragm around an opening called the pupil.
The iris has two muscles: The dilator muscle makes the iris smaller and therefore the pupil larger, allowing more light into the eye; the sphincter muscle makes the iris larger and the pupil smaller, allowing less light into the eye. Pupil size can change from 2 millimeters to 8 millimeters. This means that by changing the size of the pupil, the eye can change the amount of light that enters it by 30 times. The innermost layer is the retina -- the light-sensing portion of the eye. It contains rod cells, which are responsible for vision in low light, and cone cells, which are responsible for color vision and detail. In the back of the eye, in the center of the retina, is the macula. In the center of the macula is an area called the fovea centralis. This area contains only cones and is responsible for seeing fine detail clearly. The retina contains a chemical called rhodopsin, or "visual purple." This is the chemical that converts light into electrical impulses that the brain interprets as vision. The retinal nerve fibers collect at the back of the eye and form the optic nerve, which conducts the electrical impulses to the brain. The spot where the optic nerve and blood vessels exit the retina is called the optic disk. This area is a blind spot on the retina because there are no rods or cones at that location. However, you are not aware of this blind spot because each eye covers for the blind spot of the other eye. When a doctor looks at the back of your eye through an ophthalmoscope, here's the view:
Inside the eyeball there are two fluid-filled sections separated by the lens. The larger, back section contains a clear, gel-like material called vitreous humor. The smaller, front section contains a clear, watery material called aqueous humor. The aqueous humor is divided into two sections called the anterior chamber (in front of the iris) and the posterior chamber (behind the iris). The aqueous humor is produced in the ciliary body and is drained through the canal of Schlemm. When this drainage is blocked, a disease called glaucoma can result. The lens is a clear, bi-convex structure about 10 mm (0.4 inches) in diameter. The lens changes shape because it is attached to muscles in the ciliary body. The lens is used to fine-tune vision. Covering the inside surface of the eyelids and sclera is a mucous membrane called the conjunctiva, which helps to keep the eye moist. An infection of this area is called conjunctivitis (also called pink eye). The eye is unique in that it is able to move in many directions to maximize the field of vision, yet is protected from injury by a bony cavity called the orbital cavity. The eye is embedded in fat, which provides some cushioning. The eyelids protect the eye by blinking. This also keeps the surface of the eye moist by spreading tears over the eyes. Eyelashes and eyebrows protect the eye from particles that may injure it. Tears are produced in the lacrimal glands, which are located above the outer segment of each eye. The tears eventually drain into the inner corner of the eye, into the lacrimal sac, then through the nasal duct and into the nose. That is why your nose runs when you cry. There are six muscles attached to the sclera that control the movements of the eye. They are shown here:
Muscle
Primary Function
Medial rectus
moves eye towards nose
Lateral rectus
moves eye away from nose
Superior rectus
raises eye
Inferior rectus
lowers eye
Superior oblique
rotates eye
Inferior oblique
rotates eye
Perceiving Light
When light enters the eye, it first passes through the cornea, then the aqueous humor, lens and vitreous humor. Ultimately it reaches the retina, which is the light-sensing structure of the eye. The retina contains two types of cells, called rods and cones. Rods handle vision in low light, and cones handle color vision and detail. When light contacts these two types of cells, a series of complex chemical reactions occurs. The chemical that is formed (activated rhodopsin) creates electrical impulses in the optic nerve. Generally, the outer segment of rods are long and thin, whereas the outer segment of cones are more, well, cone shaped. Below is an example of a rod and a cone:
The outer segment of a rod or a cone contains the photosensitive chemicals. In rods, this chemical is called rhodopsin; in cones, these chemicals are called color pigments. The retina contains 100 million rods and 7 million cones. The retina is lined with black pigment called melanin -- just as the inside of a camera is black -- to lessen the amount of reflection. The retina has a central area, called the macula, that contains a high concentration of only cones. This area is responsible for sharp, detailed vision. When light enters the eye, it comes in contact with the photosensitive chemical rhodopsin (also called visual purple). Rhodopsin is a mixture of a protein called scotopsin and 11-cis-retinal -- the latter is derived from vitamin A (which is why a lack of vitamin A causes vision problems). Rhodopsin decomposes when it is exposed to light because light causes a physical change in the 11-cis-retinal portion of the rhodopsin, changing it to all-trans retinal. This first reaction takes only a few trillionths of a second. The 11-cis-retinal is an angulated molecule, while all-trans retinal is a straight molecule. This makes the chemical unstable. Rhodopsin breaks down into several intermediate compounds, but eventually (in less than a second) forms metarhodopsin II (activated rhodopsin). This chemical causes electrical impulses that are transmitted to the brain and interpreted as light. Here is a diagram of the chemical reaction we just discussed:
Activated rhodopsin causes electrical impulses in the following way:
The cell membrane (outer layer) of a rod cell has an electric charge. When light activates rhodopsin, it causes a reduction in cyclic GMP, which causes this electric charge to increase. This produces an electric current along the cell. When more light is detected, more rhodopsin is activated and more electric current is produced.
This electric impulse eventually reaches a ganglion cell, and then the optic nerve.
The nerves reach the optic chasm, where the nerve fibers from the inside half of each retina cross to the other side of the brain, but the nerve fibers from the outside half of the retina stay on the same side of the brain.
These fibers eventually reach the back of the brain (occipital lobe). This is where vision is interpreted and is called the primary visual cortex. Some of the visual fibers go to other parts of the brain to help to control eye movements, response of the pupils and iris, and behavior.
Eventually, rhodopsin needs to be re-formed so that the process can recur. The all-trans retinal is converted to 11-cis-retinal, which then recombines with scotopsin to form rhodopsin to begin the process again when exposed to light.
Color Vision
The color-responsive chemicals in the cones are called cone pigments and are very similar to the chemicals in the rods. The retinal portion of the chemical is the same, however the scotopsin is replaced with photopsins. Therefore, the color-responsive pigments are made of retinal and photopsins. There are three kinds of color-sensitive pigments:
Red-sensitive pigment
Green-sensitive pigment
Blue-sensitive pigment
Each cone cell has one of these pigments so that it is sensitive to that color. The human eye can sense almost any gradation of color when red, green and blue are mixed.
In the diagram above, the wavelengths of the three types of cones (red, green and blue) are shown. The peak absorbancy of blue-sensitive pigment is 445 nanometers, for green-sensitive pigment it is 535 nanometers, and for red-sensitive pigment it is 570 nanometers.
Color Blindness
Color blindness is the inability to differentiate between different colors. The most common type is red-green color blindness. This occurs in 8 percent of males and 0.4 percent of females. It occurs when either the red or green cones are not present or not functioning properly. People with this problem are not completely unable to see red or green, but often confuse the two colors. This is an inherited disorder and affects men more commonly since the capacity for color vision is located on the X chromosome. (Women have two X chromosomes, so the probability of inheriting at least one X with normal color vision is high; men have only one X chromosome to work with.). The inability to see any color, or seeing only in different shades of gray, is very rare.
Vitamin A Deficiency
When severe vitamin A deficiency is present, then night blindness occurs. Vitamin A is necessary to form retinal, which is part of the rhodopsin molecule. When the levels of light-sensitive molecules are low due to vitamin A deficiency, there may not be enough light at night to permit vision. During daylight, there is enough light stimulation to produce vision despite low levels of retinal.
Refraction
When light rays reach an angulated surface of a different material, it causes the light rays to bend. This is called refraction. When light reaches a convex lens, the light rays bend toward the center:
When light rays reach a concave lens, the light rays bend away from the center:
The eye has multiple angulated surfaces that cause light to bend. These are:
The interface between the air and the front of the cornea
The interface between the back of the cornea and the aqueous humor
The interface between the aqueous humor and the front of the lens
The interface between the back of the lens and the vitreous humor
When everything is working correctly, light makes it through these four interfaces and arrives at the retina in perfect focus.
Normal Vision
Vision or visual acuity is tested by reading a Snellen eye chart at a distance of 20 feet. By looking at lots of people, eye doctors have decided what a "normal" human being should be able to see when standing 20 feet away from an eye chart. If you have 20/20 vision, it means that when you stand 20 feet away from the chart you can see what a "normal" human being can see. (In metric, the standard is 6 meters and it's called 6/6 vision). In other words, if you have 20/20 vision your vision is "normal" -- a majority of people in the population can see what you can see at 20 feet. If you have 20/40 vision, it means that when you stand 20 feet away from the chart you can only see what a normal human can see when standing 40 feet from the chart. That is, if there is a "normal" person standing 40 feet away from the chart, and you are standing only 20 feet away from the chart, you and the normal person can see the same detail. 20/100 means that when you stand 20 feet from the chart you can only see what a normal person standing 100 feet away can see. 20/200 is the cutoff for legal blindness in the United States. You can also have vision that is better than the norm. A person with 20/10 vision can see at 20 feet what a normal person can see when standing 10 feet away from the chart. Hawks, owls and other birds of prey have much more acute vision than humans. A hawk has a much smaller eye than a human being but has lots of sensors (cones) packed into that space. This gives a hawk vision that is eight times more acute than a human's. A hawk might have 20/2 vision!
Errors of Refraction
Normally, your eye can focus an image exactly on the retina:
Nearsightedness and farsightedness occur when the focusing is not perfect. When nearsightedness (myopia) is present, a person is able to see near objects well and has difficulty seeing objects that are far away. Light rays become focused in front of the retina. This is caused by an eyeball that is too long, or a lens system that has too much power to focus. Nearsightedness is corrected with a concave lens. This lens causes the light to diverge slightly before it reaches the eye, as seen here:
When farsightedness (hyperopia) is present, a person is able to see distant objects well and has difficulty seeing objects that are near. Light rays become focused behind the retina. This is caused by an eyeball that is too short, or by a lens system that has too little focusing power. This is corrected with a convex lens, as seen here:
Astigmatism
Astigmatism is an uneven curvature of the cornea and causes a distortion in vision. To correct this, a lens is shaped to correct the unevenness. Why does vision worsen as we age? As we grow older, the lens becomes less elastic. It loses its ability to change shape. This is called presbyopia and is more noticeable when we try to see things that are close up, because the ciliary body must contract to make the lens thicker. The loss of elasticity prevents the lens from becoming thicker. As a result, we lose the ability to focus on close objects. At first, people begin holding things farther away in order to see them in focus. This usually becomes noticeable when we reach our mid-forties. Eventually, the lens is unable to move and becomes more or less permanently focused at a fixed distance (which is different for each person). To correct this, bifocals are required. Bifocals are a combination of a lower lens for close vision (reading) and an upper lens for distance vision.
Depth Perception
The eye uses three methods to determine distance:
The size a known object has on your retina - If you have knowledge of the size of an object from previous experience, then your brain can gauge the distance based on the size of the object on the retina.
Moving parallax - When you move your head from side to side, objects that are close to you move rapidly across your retina. However, objects that are far away move very little. In this way, your brain can tell roughly how far something is from you.
Stereo vision - Each eye receives a different image of an object on its retina because each eye is about 2 inches apart. This is especially true when an object is close to your eyes. This is less useful when objects are far away because the images on the retina become more identical the farther they are from your eyes.
Blindness
Legal blindness is usually defined as visual acuity less than 20/200 with corrective lenses. Now that you have learned some anatomy of the eye and how it functions, it becomes easier to understand how the following conditions can lead to blindness:
Cataracts - This is a cloudiness in the lens that blocks light from reaching the retina. It becomes more common as we age, but babies can be born with a cataract. As it worsens, it can require surgery to remove the lens and place an intraocular lens.
Glaucoma - If the aqueous humor does not drain out correctly, then pressure builds up in the eye. This causes the cells and nerve fibers in the back of the eye to die. This can be treated with medications and surgery.
Diabetic retinopathy - Persons with diabetes can get blockage of blood vessels, leakage of blood vessels and scarring that can lead to blindness. This can be treated with laser surgery.
Macular degeneration - In some persons, the macula (which is responsible for fine detail in the center of vision) can deteriorate with age for unknown reasons. This causes loss of central vision. This can sometimes be helped with laser surgery.
Trauma - Direct trauma or chemical injuries can cause enough damage to the eyes to prevent adequate vision.
Retinitis pigmentosa - This is an inherited disease that causes a degeneration of the retina and excess pigment. It first causes night blindness and then tunnel vision, which often gradually progresses to total blindness. There is no known treatment.
Trachoma - This is an infection caused by an organism called Chlamydia trachomatis. It is a common cause of blindness worldwide but is rare in the United States. It can be treated with antibiotics.
Mass-produced holograms often look more like green photographs than 3-D images.
If you want to see a hologram, you don't have to look much farther than your wallet. There are holograms on most driver's licenses, ID cards and credit cards. If you're not old enough to drive or use credit, you can still find holograms around your home. They're part of CD, DVD and software packaging, as well as just about everything sold as "official merchandise."
Unfortunately, these holograms -- which exist to make forgery more difficult -- aren't very impressive. You can see changes in colors and shapes when you move them back and forth, but they usually just look like sparkly pictures or smears of color. Even the mass-produced holograms that feature movie and comic book heroes can look more like green photographs than amazing 3-D images. On the other hand, large-scale holograms, illuminated with lasers or displayed in a darkened room with carefully directed lighting, are incredible. They're two-dimensional surfaces that show absolutely precise, three-dimensional images of real objects. You don't even have to wear special glasses or look through a View-Master to see the images in 3-D. If you look at these holograms from different angles, you see objects from different perspectives, just like you would if you were looking at a real object. Some holograms even appear to move as you walk past them and look at them from different angles. Others change colors or include views of completely different objects, depending on how you look at them.
If you tear a hologram in half, you can still see the whole image in each piece. The same is true with smaller and smaller pieces.
Holograms have other surprising traits as well. If you cut one in half, each half contains whole views of the entire holographic image. The same is true if you cut out a small piece -- even a tiny fragment will still contain the whole picture. On top of that, if you make a hologram of a magnifying glass, the holographic version will magnify the other objects in the hologram, just like a real one.
Once you know the principles behind holograms, understanding how they can do all this is easy. This article will explain how a hologram, light and your brain work together make clear, 3-D images. All of a hologram's properties come directly from the process used to create it, so we'll start with an overview of what it takes to make one.
Making a Hologram
Transmission and Reflection
There are two basic categories of holograms -- transmission and reflection. Transmission holograms create a 3-D image when monochromatic light, or light that is all one wavelength, travels through them. Reflection holograms create a 3-D image when laser light or white light reflects off of their surface. For the sake of simplicity, this article discusses transmission holograms viewed with the help of a laser except where noted.
It doesn't take very many tools to make a hologram. You can make one with:
A laser: Red lasers, usually helium-neon (HeNe) lasers, are common in holography. Some home holography experiments rely on the diodes from red laser pointers, but the light from a laser pointer tends to be less coherent and less stable, which can make it hard to get a good image. Some types of holograms use lasers that produce different colors of light as well. Depending on the type of laser you're using, you may also need a shutter to control the exposure.
Lenses: Holography is often referred to as "lensless photography," but holography does require lenses. However, a camera's lens focuses light, while the lenses used in holography cause the beam to spread out.
A beam splitter: This is a device that uses mirrors and prisms to split one beam of light into two beams.
Mirrors: These direct the beams of light to the correct locations. Along with the lenses and beam splitter, the mirrors have to be absolutely clean. Dirt and smudges can degrade the final image.
Holographic film: Holographic film can record light at a very high resolution, which is necessary for creating a hologram. It's a layer of light-sensitive compounds on a transparent surface, like photographic film. The difference between holographic and photographic film is that holographic film has to be able to record very small changes in light that take place over microscopic distances. In other words, it needs to have a very fine grain. In some cases, holograms that use a red laser rely on emulsions that respond most strongly to red light.
There are lots of different ways to arrange these tools -- we'll stick to a basic transmission hologram setup for now.
The laser points at the beam splitter, which divides the beam of light into two parts.
Mirrors direct the paths of these two beams so that they hit their intended targets.
Each of the two beams passes through a diverging lens and becomes a wide swath of light rather than a narrow beam.
One beam, the object beam, reflects off of the object and onto the photographic emulsion.
The other beam, the reference beam, hits the emulsion without reflecting off of anything other than a mirror.
Workspace Requirements
Since holography typically uses red lasers, red darkroom safelights like this one may interfere with the final image.
Getting a good image requires a suitable work space. In some ways, the requirements for this space are more stringent than the requirements for your equipment. The darker the room is, the better. A good option for adding a little light to the room without affecting the finished hologram is a safelight, like the ones used in darkrooms. Since darkroom safelights are often red and holography often uses red light, there are green and blue-green safelights made specifically for holography. Holography also requires a working surface that can keep the equipment absolutely still -- it can't vibrate when you walk across the room or when cars drive by outside. Holography labs and professional studios often use specially designed tables that have honeycomb-shaped support layers resting on pneumatic legs. These are under the table's top surface, and they dampen vibration. You can make your own holography table by placing inflated inner tubes on a low table, then placing a box full of a thick layer of sand on top of it. The sand and the inner tubes will play the role of the professional table's honeycombs and pneumatic supports. If you don't have enough space for such a large table, you can improvise using cups of sand or sugar to hold each piece of equipment, but these won't be as steady as a larger setup.
To make clear holograms, you need to reduce vibration in the air as well. Heating and air conditioning systems can blow the air around, and so can the movement of your body, your breath and even the dissipation of your body heat. For these reasons, you'll need to turn the heating and cooling system off and wait for a few minutes after setting up your equipment to make the hologram.
These precautions sound a little like photography advice taken to the extreme -- when you take pictures with a camera, you have to keep your lens clean, control light levels and hold the camera absolutely still. This is because making a hologram is a lot like taking a picture with a microscopic level of detail. We'll look at how holograms are like photographs .
Holograms and Photographs
When you take a picture with a film camera, four basic steps happen in an instant:
A shutter opens.
Light passes through a lens and hits the photographic emulsion on a piece of film.
A light-sensitive compound called silver halide reacts with the light, recording its amplitude, or intensity, as it reflects off of the scene in front of you.
The shutter closes.
You can make lots of changes to this process, like how far the shutter opens, how much the lens magnifies the scene and how much extra light you add to the mix. But no matter what changes you make, the four basic steps are still the same. In addition, regardless of changes to the setup, the resulting picture is still simply a recording of the intensity of reflected light. When you develop the film and make a print of the picture, your eyes and brain interpret the light that reflects from the picture as a representation of the original image. You can learn more about the process in How Vision Works, How Cameras Work and How Film Works.
In photography, light passes through a lens and a shutter before hitting a piece of film or a light-sensitive sensor.
Like photographs, holograms are recordings of reflected light. Making them requires steps that are similar to what it takes to make a photograph:
A shutter opens or moves out of the path of a laser. (In some setups, a pulsed laser fires a single pulse of light, eliminating the need for a shutter.)
The light from the object beam reflects off of an object. The light from the reference beam bypasses the object entirely.
The light from both beams comes into contact with the photographic emulsion, where light-sensitive compounds react to it.
The shutter closes, blocking the light.
In holography, light passes through a shutter and lenses before striking a light-sensitive piece of holographic film.
Just like with a photograph, the result of this process is a piece of film that has recorded the incoming light. However, when you develop the holographic plate and look at it, what you see is a little unusual. Developed film from a camera shows you a negative view of the original scene -- areas that were light are dark, and vice versa. When you look at the negative, you can still get a sense of what the original scene looked like.
But when you look at a developed piece of film used to make a hologram, you don't see anything that looks like the original scene. Instead, you might see a dark frame of film or a random pattern of lines and swirls. Turning this frame of film into an image requires the right illumination. In a transmission hologram, monochromatic light shines through the hologram to make an image. In a reflection hologram, monochromatic or white light reflects off of the surface of the hologram to make an image. Your eyes and brain interpret the light shining through or reflecting off of the hologram as a representation of a three-dimensional object. The holograms you see on credit cards and stickers are reflection holograms.
You need the right light source to see a hologram because it records the light's phase and amplitude like a code. Rather than recording a simple pattern of reflected light from a scene, it records the interference between the reference beam and the object beam. It does this as a pattern of tiny interference fringes. Each fringe can be smaller than one wavelength of the light used to create them. Decoding these interference fringes requires a key -- that key is the right kind of light.
Next, we'll explore exactly how light makes interference fringes.
Holograms and Light
To understand how interference fringes form on film, you need to know a little bit about light. Light is part of the electromagnetic spectrum -- it's made of high-frequency electrical and magnetic waves. These waves are fairly complex, but you can imagine them as similar to waves on water. They have peaks and troughs, and they travel in a straight line until they encounter an obstacle. Obstacles can absorb or reflect light, and most objects do some of both. Reflections from completely smooth surfaces are specular, or mirror-like, while reflections from rough surfaces are diffuse, or scattered.
The wavelength of light is the distance from one peak of the wave to the next. This relates to the wave's frequency, or the number of waves that pass a point in a given period of time. The frequency of light determines its color and is measured in cycles per second, or Hertz (Hz). Colors at the red end of the spectrum have lower frequencies, while colors at the violet end of the spectrum have higher frequencies. Light's amplitude, or the height of the waves, corresponds to its intensity.
Light reflection can be specular, mirror-like (left), diffuse or scattered.
White light, like sunlight, contains all of the different frequencies of light traveling in all directions, including ones that are beyond the visible spectrum. Although this light allows you to see everything around you, it's relatively chaotic. It contains lots of different wavelengths traveling in lots of different directions. Even waves of the same wavelength can be in a different phase, or alignment between the peaks and troughs.
Laser light, on the other hand, is orderly. Lasers produce monochromatic light -- it has one wavelength and one color. The light that emerges from a laser is also coherent. All of the peaks and troughs of the waves are lined up, or in phase. The waves line up spatially, or across the wave of the beam, as well as temporally, or along the length of the beam. You can check out How Lasers Work to see precisely how a laser does this.
Next we'll look at light reflection and redundancy.
Light Reflection
Redundancy
If you tore a hologram of a mask in half, you could still see the whole mask in each half. But by removing half of the hologram, you also remove half of the information required to recreate the scene. For this reason, the resolution of the image you see in half a hologram isn’t as good. In addition, the holographic plate doesn’t get information about areas that are out of its line of sight, or physically blocked by the surface of the object.
You can make and view a photograph using unorganized white light, but to make a hologram, you need the organized light of a laser. This is because photographs record only the amplitude of the light that hits the film, while holograms record differences in both amplitude and the phase. In order for the film to record these differences, the light has to start out with one wavelength and one phase across the entire beam. All the waves have to be identical when they leave the laser. Here's what happens when you turn on a laser to expose a holographic plate:
A column of light leaves the laser and passes through the beam splitter.
The two columns reflect off of their respective mirrors and pass through their respective diverging lenses.
The object reflects off of the object and combines with the reference beam at the holographic film.
There are a couple of things to keep in mind about the object beam. One is that the object is not 100 percent reflective -- it absorbs some of the laser light that reaches it, changing the intensity of the object wave. The darker portions of the object absorb more light, and the lighter portions absorb less light.
When light waves reflect, they follow the law of reflection. The angle at which they strike the surface is the same as the angle at which they leave it.
On top of that, the surface of the object is rough on a microscopic level, even if it looks smooth to the human eye, so it causes a diffuse reflection. It scatters light in every direction following the law of reflection. In other words, the angle of incidence, or the angle at which the light hits the surface, is the same as its angle of reflection, or the light at which it leaves the surface. This diffuse reflection causes light reflected from every part of the object to reach every part of the holographic plate. This is why a hologram is redundant -- each portion of the plate holds information about each portion of the object. The holographic plate captures the interaction between the object and reference beams. We'll look at how this happens .
Capturing the Fringes
The light-sensitive emulsion used to create holograms makes a record of the interference between the light waves in the reference and object beams. When two wave peaks meet, they amplify each other. This is constructive interference. When a peak meets a trough, they cancel one another out. This is destructive interference. You can think of the peak of a wave as a positive number and the trough as a negative number. At every point at which the two beams intersect, these two numbers add up, either flattening or amplifying that portion of the wave.
This a lot like what happens when you transmit information using radio waves. In amplitude modulation (AM) radio transmissions, you combine a sine wave with a wave of varying amplitudes. In frequency modulation (FM) radio transmissions, you combine a sine wave with a wave of varying frequencies. Either way, the sine wave is the carrier wave that is overlaid with a second wave that carries the information.
In a hologram, the two intersecting light wave fronts form a pattern of hyperboloids -- three-dimensional shapes that look like hyperbolas rotated around one or more focal points. You can read more about hyperboloidal shapes at Wolfram Math World.
The holographic plate, resting where the two wave fronts collide, captures a cross-section, or a thin slice, of these three-dimensional shapes. If this sounds confusing, just imagine looking through the side of a clear aquarium full of water. If you drop two stones into the water at opposite ends of the aquarium, waves will spread toward the center in concentric rings. When the waves collide, they will constructively and destructively interfere with each other. If you took a picture of this aquarium and covered up all but a thin slice in the middle, what you'd see is a cross-section of the interference between two sets of waves in one specific location.
You can visualize the interaction of light waves by imagining waves on water.
The light that reaches the holographic emulsion is just like the waves in the aquarium. It has peaks and troughs, and some of the waves are taller while others are shorter. The silver halide in the emulsion responds to these light waves just like it responds to light waves in an ordinary photograph. When you develop the emulsion, parts of the emulsion that receive more intense light get darker, while those that receive less intense light stay a little lighter. These darker and lighter areas become the interference fringes.
Bleaching the Emulsion
Holographic Magnifying Glass
If you make a hologram of a scene that includes a magnifying glass, the light from the object beam passes through the glass on its way to the emulsion. The magnifying glass spreads out the laser light, just like it would with ordinary light. This spread-out light is what forms part of the interference pattern on the emulsion. You can also use the holographic process to magnify images by positioning the object farther from the holographic plate. The light waves reflected off of the object can spread out farther before they reach the plate. You can magnify a displayed hologram by using a laser with a longer wavelength to illuminate it.
The amplitude of the waves corresponds to the contrast between the fringes. The wavelength of the waves translates to the shape of each fringe. Both the spatial coherence and the contrast are a direct result of the laser beam's reflection off of the object. Turning these fringes back into images requires light. The trouble is that all the tiny, overlapping interference fringes can make the hologram so dark that it absorbs most of the light, letting very little pass through for image reconstruction. For this reason, processing holographic emulsion often requires bleaching using a bleach bath. Another alternative is to use a light-sensitive substance other than silver halide, such as dichromated gelatin, to record the interference fringes.
Once a hologram is bleached, it is clear instead of dark. Its interference fringes still exist, but they have a different index of refraction rather than a darker color. The index of refraction is the difference between how fast light travels through a medium and how fast it travels through a vacuum. For example, the speed of a wave of light can change as it travels through air, water, glass, different gasses and different types of film. Sometimes, this produces visible distortions, like the apparent bending of a spoon placed in a half-full glass of water. Differences in the index of refraction also cause rainbows on soap bubbles and on oil stains in parking lots. In a bleached hologram, variations in the index of refraction change how the light waves travel through and reflect off of the interference fringes.
These fringes are like a code. It takes your eyes, your brain and the right kind of light to decode them into an image.
Decoding the Fringes
The microscopic interference fringes on a hologram don't mean much to the human eye. In fact, since the overlapping fringes are both dark and microscopic, all you're likely to see if you look at the developed film of a transmission hologram is a dark square. But that changes when monochrome light passes through it. Suddenly, you see a 3-D image in the same spot where the object was when the hologram was made.
In a transmission hologram, the light illuminating the hologram comes from the side opposite the observer.
A lot of events take place at the same time to allow this to happen. First, the light passes through a diverging lens, which causes monochromatic light -- or light that consists of one wavelength color -- to hit every part of the hologram simultaneously. Since the hologram is transparent, it transmits a lot of this light, which passes through unchanged.
Regardless of whether they are dark or clear, the interference fringes reflect some of the light. This is where things get interesting. Each interference fringe is like a curved, microscopic mirror. Light that hits it follows the law of reflection, just like it did when it bounced off the object to create the hologram in the first place. Its angle of incidence equals its angle of reflection, and the light begins to travel in lots of different directions.
The interference fringes in a hologram cause light to scatter in all directions, creating an image in the process. The fringes diffract and reflect some of the light (inset), and some of the light passes through unchanged.
But that's only part of the process. When light passes around an obstacle or through a slit, it undergoes diffraction, or spreads out. The more a beam of light spreads out from its original path, the dimmer it becomes along the edges. You can see what this looks like using an aquarium with a slotted panel placed across its width. If you drop a pebble into one end of the aquarium, waves will spread toward the panel in concentric rings. Only a little piece of each ring will make it through each gap in the panel. Each of those little pieces will go on spreading on the other side.
This process is a direct result of the light traveling as a wave -- when a wave moves past an obstacle or through a slit, its wave front expands on the other side. There are so many slits among the interference fringes of a hologram that it acts like a diffraction grating, causing lots of intersecting wave fronts to appear in a very small space.
Recreating the Object Beam
The diffraction grating and reflective surfaces inside the hologram recreate the original object beam. This beam is absolutely identical to the original object beam before it was combined with the reference wave. This is what happens when you listen to the radio. Your radio receiver removes the sine wave that carried the amplitude- or frequency-modulated information. The wave of information returns to its original state, before it was combined with the sine wave for transmission. The beam also travels in the same direction as the original object beam, spreading out as it goes. Since the object was on the other side of the holographic plate, the beam travels toward you. Your eyes focus this light, and your brain interprets it as a three-dimensional image located behind the transparent hologram. This may sound far-fetched, but you encounter this phenomenon every day. Every time you look in a mirror, you see yourself and the surroundings behind you as though they were on the other side of the mirror's surface. But the light rays that make this image aren't on the other side of the mirror -- they're the ones that bounce off of the mirror's surface and reach your eyes. Most holograms also act like color filters, so you see the object as the same color as the laser used in its creation rather than its natural color. This virtual image comes from the light that hits the interference fringes and spreads out on the way to your eyes. However, light that hits the reverse side of each fringe does the opposite. Instead of moving upward and diverging, it moves downward and converges. It turns into a focused reproduction of the object -- a real image that you can see if you put a screen in its path. The real image is pseudoscopic, or flipped back to front -- it's the opposite of the virtual image that you can see without the aid of a screen. With the right illumination, holograms can display both images at the same time. However, in some cases, whether you see the real or the virtual image depends on what side of the hologram is facing you.
Your brain plays a big role in your perception of both of these images. When your eyes detect the light from the virtual image, your brain interprets it as a beam of light reflected from a real object. Your brain uses multiple cues, including, shadows, the relative positions of different objects, distances and parallax, or differences in angles, to interpret this scene correctly. It uses these same cues to interpret the pseudoscopic real image.
This description applies to transmission holograms made with silver halide emulsion. Next, we'll look at some other types of holograms.
Other Hologram Types
The holograms you can buy as novelties or see on your driver's license are reflection holograms. These are usually mass-produced using a stamping method. When you develop a holographic emulsion, the surface of the emulsion collapses as the silver halide grains are reduced to pure silver. This changes the texture of the emulsion's surface. One method of mass-producing holograms is coating this surface in metal to strengthen it, then using it to stamp the interference pattern into metallic foil. A lot of the time, you can view these holograms in normal white light. You can also mass-produce holograms by printing them from a master hologram, similar to the way you can create lots of photographic prints from the same negative.
The holograms found on credit cards and other everyday objects are mass-produced by stamping the pattern of the hologram onto the foil.
But reflection holograms can also be as elaborate as the transmission holograms we already discussed. There are lots of object and laser setups that can produce these types of holograms. A common one is an inline setup, with the laser, the emulsion and the object all in one line. The beam from the laser starts out as the reference beam. It passes through the emulsion, bounces off the object on the other side, and returns to the emulsion as the object beam, creating an interference pattern. You view this hologram when white or monochrome light reflects off of its surface. You're still seeing a virtual image -- your brain's interpretation of light waves that seem to be coming from a real object on the other side of the hologram.
Reflection holograms are often thicker than transmission holograms. There is more physical space for recording interference fringes. This also means that there are more layers of reflective surfaces for the light to hit. You can think of holograms that are made this way as having multiple layers that are only about half a wavelength deep. When light enters the first layer, some of it reflects back toward the light source, and some continues to the next layer, where the process repeats. The light from each layer interferes with the light in the layers above it. This is known as the Bragg effect, and it's a necessary part of the reconstruction of the object beam in reflection holograms. In addition, holograms with a strong Bragg effect are known as thick holograms, while those with little Bragg effect are thin.
The Bragg effect can also change the way the hologram reflects light, especially in holograms that you can view in white light. At different viewing angles, the Bragg effect can be different for different wavelengths of light. This means that you might see the hologram as one color from one angle and another color from another angle. The Bragg effect is also one of the reasons why most novelty holograms appear green even though they were created with a red laser.
Multiple Images
In movies, holograms can appear to move and recreate entire animated scenes in midair, but today's holograms can only mimic movement. You can get the illusion of movement by exposing one holographic emulsion multiple times at different angles using objects in different positions. The hologram only creates each image when light strikes it from the right angle. When you view this hologram from different angles, your brain interprets the differences in the images as movement. It's like you're viewing a holographic flip book. You can also use a pulsed laser that fires for a minute fraction of a second to make still holograms of objects in motion.
The famous hologram "The Kiss" shows a sequence of similar, stationary images. Your eye sees many frames simultaneously, and your brain interprets them as moving images.
Multiple exposures of the same plate can lead to other effects as well. You can expose the plate from two angles using two completely different images, creating one hologram that displays different images depending on viewing angle. Exposing the same plate using the exact same scene and red, green and blue lasers can create a full-color hologram. This process is tricky, though, and it's not usually used for mass-produced holograms. You can also expose the same scene before and after the subject has experienced some kind of stimulus, like a gust of wind or a vibration. This lets researchers see exactly how the stimulus changed the object.
The First Hologram:
Dennis Gabor invented holograms in 1947. He was attempting to find a method for improving the resolution of electron microscopes. However, lasers, which are necessary for creating and displaying good holograms, were not invented until 1960. Gabor used a mercury vapor lamp, which produced monochrome blue light, and filters make his light more coherent. Gabor won the Nobel Prize in Physics for his invention in 1971.
Using lasers to make three-dimensional images of objects may sound like a novelty or a form of art. But holograms have an increasing number of practical uses. Scientists can use holograms to study objects in three dimensions, and they can use acoustical holography to create three-dimensional reconstructions of sound waves. Holographic memory has also become an increasingly common method of storing large amounts of data in a very small space. Some researchers even believe that the human brain stores information in a manner that is much like a hologram. Although holograms don't currently move like they do in the movies, researchers are studying ways to project fully 3-D holograms into visible air. In the future, you may be able to use holograms to do everything from watching TV to deciding which hair style will look best on you.
Microsoft's first video game console, the Xbox, has sold more than 20 million units worldwide since its introduction in 2001. Despite the Xbox's impressive power, the list of big-name video game titles to support it and the success of the Xbox's online component, Xbox LIVE, Sony's PlayStation 2 still outsold it.
As the game industry moved into the next generation of video game technology, Microsoft was determined to dethrone Sony's PlayStation. Enter the Xbox 360.
Photo courtesy Microsoft Corp. Xbox 360.
Microsoft rebuilt the Xbox from the ground up. From the name to the look to hardware and features, the Xbox 360 is a radically different and more powerful machine than its predecessor. Far more than a video game console, the Xbox 360 is a total media center that allows users to play, network, rip, stream and download all types of media, including high-definition movies, music, digital pictures and game content. In this article, we will learn about the hardware and features that make the Xbox 360 a leap forward into the next generation of gaming consoles.
The Xbox 360, like all video game consoles, is just a computer with hardware and software dedicated to the function of running video game software. The original Xbox was essentially a Windows PC with a modified Pentium III processor, some relatively powerful graphics and audio hardware and a modified version of the Microsoft operating system Windows 2000, all packaged in that distinctive black box. The Xbox 360 is also a specially packaged computer, but once you look inside, you realize that this console has quite a bit under the hood:
Custom IBM Power PC-based CPU with three 3.2 GHz cores
Custom ATI graphics processor with 10 MB embedded DRAM
512 MB 700 MHz GDDR3 RAM
Detachable and upgradeable hard drive -- all models except the Core system
12x dual-layer DVD-ROM
Support for up to four wireless game controllers
Three USB 2.0 ports
Two memory unit slots
As you can see, Microsoft intends the Xbox 360 to be a serious game machine. The company is also serious about reaching more audiences with the Xbox 360. On the next , we'll look at variations of the Xbox 360 that are marketed to different kinds of gamers.
Xbox 360 Consoles
Microsoft released two versions of the Xbox 360 in November 2005: the Xbox 360 Premium Package and Xbox 360 Core System. Since then, the lineup has undergone some changes. The Premium Package is now known simply as the Xbox 360 console. A new Elite system hit store shelves in April 2007. Microsoft announced another new system, the Xbox 360 Arcade, in October 2007.
The Xbox 360 debuted at the 2005 E3 Expo Microsoft booth.
The Core System is "plug and play" -- in addition to the console, it includes a wired controller and an AV cable. The Xbox 360 comes with a wireless controller, an HD AV cable, an Ethernet connectivity cable, a headset and a removable 20-GB hard drive. Initially, it also included a DVD remote, but this is no longer available as part of the package. The Xbox 360 Elite is similar to the main Xbox 360, with a black case, matching wireless controller and headset. It also includes a larger 120-GB hard drive and an HDMI cable. To combat Nintendo's surprise powerhouse, the Wii, Microsoft announced the Xbox 360 Arcade in October 2007. Aimed at casual gamers, the console will come with between three and five Xbox LIVE Arcade games and will probably include "Pac-Man," "Uno" and "Luxor 2." Microsoft has also prepared subtle variations of the console for marketing tie-ins. To commemorate the release of "The Simpsons Movie," Microsoft created a run of 100 limited-edition Simpsons Xbox 360s, which were given away in promotions. Fans of Bungie's "Halo" game series can purchase the "Halo 3" limited edition Xbox 360, which comes in "Spartan green and gold" and features a matching controller.
On the next page we will see what makes the Xbox 360 tick -- the central processing unit, or CPU.
Xbox Sales
Because of delays in manufacturing, there were not enough Xbox 360s to meet the demand of the 2005 holiday season. As a result, Xbox 360s were selling for as much as $2,000 on Web sites like eBay, and initial sales figures were poor. However, Microsoft still got a jump on its competitors, as the PlayStation 3 and the Nintendo Wii did not release until 2006. According to industry analyst the NPD Group, as of August 2007, the Xbox 360 sold 6.3 million Xbox 360s in the United States, to 4 million of Nintendo's Wii and 1.75 million Sony Playstation 3s.
CPU: The Heart of the 360
As with any computer, the CPU is the heart of the Xbox 360. Microsoft has outfitted the 360 with a 165-million transistor, multi-core processor running three 3.2-GHz PowerPC cores.
Each core on the chip functions as a separate processor. Recently,
hardware manufacturers have started combining several cores, or processors, onto one chip. This is a multi-core processor. Multi-core processors offer a combination of tremendous computing capabilities and efficient power consumption. They split heavy work loads over multiple powerful processors rather than giving all the work to one super-powerful processor.
The Xbox 360 on display at the 2005 E3 Expo.
The other interesting thing to note about the Xbox 360 CPU is that each core is capable of processing two threads simultaneously. Think of a thread as a set of instructions for a program's job. The core processes these instructions and does the heavy lifting to get the job done. A conventional processor can run a single execution thread. Because the Xbox 360 cores can each handle two threads at a time, the 360 CPU is the equivalent of having six conventional processors in one machine. What this means when you are playing video games is that the Xbox 360 can dedicate one core entirely to producing sound, while another may run the game's collision and physics engine. The system may allocate an entire processor just to rendering hi-def graphics. It's really up to the game developers how the system's considerable resources are used. With a multi-core processor, the system is powerful enough to pull off the computational demands needed for an amazing gaming experience without even breaking a sweat.
360 Degrees
According to J. Allard, Microsoft Corporate Vice President and chief XNA architect, in an interview with Gamespot, "If we were building another console in the 3D era, we'd just call it Xbox 2 ... So, we eliminated Xbox 2 from the list. So, the name that we came up with was Xbox 360, because we are putting the gamer at the center of the experience."
The graphics processor unit, or GPU, is responsible for the heavy-lifting for the console's beautiful, high-resolution images.
The GPU
Another powerful asset in the Xbox 360 is the Graphics Processor Unit (GPU). The Xbox 360 boasts the new, custom-built 500-MHz ATI Graphics Processor card with 10 MB of embedded DRAM. While the 500-MHZ graphics processor is powerful, and 10 MB of DRAM provides ample memory for the GPU to do its job, the most innovative thing about this card is that it is built on unified shader architecture. Shaders are computer programs that determine the final look of what you see on the screen when you're looking at computer animation. Shaders take rendered 3-D objects built on polygons (the building blocks of 3-D animation) and make them look more realistic. There are two types of shaders: pixel shaders and vertex shaders. Pixel shaders alter the lighting, color and surface of each pixel. This in turn affects the overall color, texture and shape of 3-D objects built from these pixels. Pixel shaders help "smooth out" 3-D objects, giving them a more organic texture.
The Xbox 360 with a custom, wood-grain faceplate.
Vertex shaders work by manipulating an object's position in 3-D space. "Vertex" refers to the intersection of two coordinates in space. The machine maps the position of an animated object in 3-D space by giving it a value. These values are the x, y and z coordinates. By manipulating these variables, a vertex shader creates realistic animation and special effects such as "morphing." In real-time graphics, like the kind you see in video games, shaders work with the graphics processor. The shaders make billions of computations every second to perform their specific tasks. These computations are performed in steps through a series of computational components. Think of an assembly line. In the world of hardware, these assembly lines are called pipelines. Traditionally, pixel shaders and vertex shaders have dedicated pipelines because each one has very specific and differing needs. As we learned before, the new ATI graphics card in the Xbox 360 has unified shader architecture. What that means is that now, both shader types share the same pipelines. ATI figured out a way at the hardware level to address the needs of both types of shaders using the same pipeline. The apparent advantage of sharing pipelines is to add more assembly lines, making computation that much faster. ATI claims that this unified shader architecture allows for 48 billion shader operations per second. The Xbox 360 is the first device to use this type of architecture. On the next , we'll learn about how the Xbox 360 fits in with your home entertainment system.
Jacks, Tracks and Other 360 Features
Input/Output The Xbox 360 supports up to four wireless controllers at once. It also has three USB 2.0 jacks, two in the front and one in the back that can be used to plug in wired controllers for play or wireless controllers when they need to be charged. The USB jacks can also be used to connect devices like digital cameras, MP3 players and computer keyboards to the 360 (but the keyboard can only be used for text entry, not game play). Online The Xbox 360 has an Ethernet port to hook up to a broadband connection, as well as a slot for a WiFi card. The 360 is WiFi-ready "out of the box" and the bundle includes a connectivity Ethernet cable. TV Connections The Xbox 360 comes standard with both composite and component video connections to hook up to a TV. There are also optional connections for S-Video and VGA, and the console supports some SCART-type adapters used in Europe. The Xbox 360 Core System includes a standard-definition AV cable, while the other Xbox 360 bundles come with an AV HD cable and a media remote. Audio The Xbox 360 has multi-channel surrounding sound that supports 256 channels of 48 KHz, 16-bit digital audio. The 32-bit audio processing is handled by the CPU. One of the most talked about new audio features of the Xbox 360 is customizable soundtracks. No matter what video game you are playing, you can play or stream your music during game play. Removable Hard Drive and Storage The original Xbox was quite innovative in that it had an 8-GB hard drive built into the console. The 360 takes the hard-drive concept one step further: The Xbox 360 includes a removable 20-GB hard drive, and the Xbox 360 Elite has a removable 120-GB hard drive. The Xbox 360 also supports up to two 64-MB memory cards at one time.
An Xbox 360's external hard drive
The Disc Drive In keeping with the idea that the Xbox 360 is a full media center, it sports a 12x dual-layer DVD-ROM that can read DVD-Video, DVD-ROM, DVD-R/RW, DVD+R/RW, CD-DA, CD-ROM, CD-R, CD-RW, WMA CD, MP3 CD and JPEG Photo CD. You can buy an external HD-DVD player for the Xbox 360. The 360 does not, however, support Blu-ray. Cooling The original Xbox took a lot of criticism for how large it was. The cooling system that kept the Xbox's rather hefty processor cool was the single greatest factor that contributed to the console's robust size. Microsoft changed all this for the Xbox 360. In order to fit all that hardware into the stylish and slim form factor of the Xbox 360, Microsoft devised a cooling system that combines a small, vacuum-sealed, liquid-cooled system with fans to maintain a comfortable temperature inside the 360. The system regulates the temperature of the cores and adjusts the flow of liquid and fan speed accordingly. Additionally, the cooling system monitors the core's workload: If one or more cores are not needed for the job at hand (for instance, if you are using the Xbox 360 to watch a DVD), then the unused cores are automatically turned off. Other Accessories There are dozens of accessories on the market for the Xbox 360, including headsets, wireless controllers, cooling systems, rechargeable batteries and more. You can play compatible Xbox 360 games on your Windows computer with the Wireless Gaming Receiver for Windows. The Live Vision Camera allows players to create an in-game version of themselves in select games. The Xbox 360 Wireless Racing Wheel is a force-feedback steering wheel controller with standard gamepad buttons and floor-mounted accelerator and brake pedals. The Messenger Kit attaches to Xbox 360 controllers and features a keyboard to message other players. In the next , we'll take a look at the Xbox 360 controller and how it has evolved from the original Xbox controller.
Xbox Controller
The design for the Xbox 360 controller is based largely on the one used for the original Xbox -- the Controller S.
The most noticeable difference in the Xbox 360 controllers from those for the original Xbox is that most of them are wireless. Microsoft created a proprietary technology to deal with some of the latency and bandwidth issues that can be a problem for some wireless controllers. The Xbox 360 can support up to four wireless controllers at one time. The wireless controller comes with all Xbox 360 bundles except for the Core system, which includes a wired controller with a nine-foot cable. Everything else about the design is the same. Of course, wireless controllers are available separately if you choose to upgrade.
Control Issues
When the original Xbox was released in 2001, one of the most common complaints about the new console was the controller. Gamers worldwide criticized it for being too large and having poor button spacing. In Japan, where the Xbox sales were already suffering, Japanese gamers all but refused to use the large Xbox controllers, opting instead for smaller, third-party ones. This compelled Microsoft to create a smaller, redesigned controller for Asian markets that was released in winter 2002.
Shortly after that, Microsoft released a slightly improved version of the Japanese controller in the west called the Controller S. The Controller S is now the standard Xbox controller that is shipped with all Xbox consoles.
The new Xbox 360 wireless controllers can be powered by either a pair of traditional AA battries or a rechargeable battery pack. The battery pack can be "flash charged" in a charger or "trickle charged" via a USB connection to the console, and it alerts the user when its charge is running low. The Xbox 360 controller has a Guide button in the center of its face that provides a new functionality. This button is divided into four quadrants that light up to provide gamers with different types of information during game play. (Incidentally, the "ring of light" power button on the console also provides this function.) For instance, during a split screen multiplayer match, a particular quadrant will light up to indicate to a player which part of the screen he or she is playing on at that time. The Guide button can also light up to let a player know he has received a message from another gamer. In this case, when the user pushes the button, he or she visits the Xbox dashboard (the equivalent of a PC's desktop). The dashboard provides access to features like messaging friends, downloading content, voice chat and customizing soundtracks, all while staying in the game. The controller has a standard headphone jack on the back so that the user can plug in a headset for voice communication during game play. Some wireless headsets will also work with the Xbox 360. The new Xbox 360 controller has the same basic familiar button layout as the Controller S except that a few of the auxiliary buttons have been moved. The "back" and "start" buttons have been moved to a more central position on the face of the controller, and the "white" and "black" buttons have been removed and replaced with two new shoulder buttons that are positioned over the analog triggers on the back of the controller. One of the great features of Xbox 360 is its ability to let players compete against one another online.
Xbox LIVE
Xbox LIVE is an online subscription service that allows Xbox gamers to play video games together and download additional game content using the Internet. Once online, gamers can play one another over the Internet and talk to each other in real-time using the headset (included in the bundle). Xbox LIVE has created a huge online community of gamers challenging one another worldwide. The Xbox 360 will also usher in the next generation of online game play and online community with the new, revamped Xbox LIVE.
The Xbox 360 is WiFi-ready so that gamers can jump on Xbox LIVE wirelessly.
The new Xbox LIVE has enhanced matchmaking and feedback systems as well as voice chat and video conferencing. It has a new, more seamless interface and is a generally more robust system for communicating during online gaming. Xbox LIVE on the 360 is divided into two services: Xbox LIVE Silver and Xbox LIVE Gold. Xbox LIVE Silver is a free service that ships with all Xbox 360s and allows any Xbox 360 user with a broadband connection to get online and create a gamer tag as well as a new ID type called a gamer card. The gamer card is a profile that displays a gamer's interests, skill level, competitiveness and gaming accomplishments. In addition, gamers can use Xbox LIVE Silver to chat, download content and play certain games. Xbox LIVE Silver allows gamers to access most of the features of Xbox LIVE. The one key feature missing from the free service is the ability to play multiplayer games online. In order to play in multiplayer matches online, you must upgrade to the subscription service known as Xbox LIVE Gold. The Gold service has all the functionality of Silver plus the ability to play multiplayer games. Additionally, Xbox LIVE Gold has exclusive content, tournaments and events.
Serious gamers know the Xbox 360 has a great slate of games available for it.
Xbox Games
As history has shown time and again, the latest and greatest console is nothing without great games. Microsoft has set out to create a series of blockbuster titles in-house for the Xbox 360 as well as make deals with as many third-party developers as possible. Game developers are attracted to the prospect of creating games on such a powerful canvas, and in the years to come they will find new ways to build games that push the potential of the Xbox 360. One game franchise more than any other has defined the success of the Xbox and Xbox 360: "Halo." Microsoft acquired game developer Bungie Studios in 2000 to bring the game to the original Xbox. The game took off and spawned a sequel. Then, on September 25, 2007, came "Halo 3." In 12 days, it had already surpassed the biggest-selling game in 2007, "Wii Play," selling 3.3 million copies and pushing the Xbox 360 ahead of the Wii in numbers of consoles sold for the month [source: Casamassina]. Microsoft even released a special "Halo"-themed Xbox 360 console for hard-core fans.
Halo 3 is one of the most successful video games in history by earning over 300 million dollars in first week sales. Read about some of the Halo 3 features.
The game even seems to have affected the motion picture industry. Ticket sales for the October 5, 2007, weekend only totaled $80 million, a 27 percent decrease from the same weekend the year before [source: Brodesser-Akner, Claude]. Some movie executives blame Bungie and Microsoft for stealing their sales. Below is a list of games that released with the Xbox 360. For a complete list of current and upcoming games, check out Xboc.com Games.
