A hard disk drive (HDD), commonly referred to as a hard drive, hard disk, or fixed disk drive is a non-volatile storage device which stores digitally encoded data on rapidly rotating platters with magnetic surfaces. Strictly speaking, "drive" refers to a device distinct from its medium, such as a tape drive and its tape, or a floppy disk drive and its floppy disk. Early HDDs had removable media; however, an HDD today is typically a sealed unit (except for a filtered vent hole to equalize air pressure) with fixed media.
HDDs (introduced in 1956 as data storage for an IBM accounting computer) were originally developed for use with general purpose computers. During the 1990s, the need for large-scale, reliable storage, independent of a particular device, led to the introduction of embedded systems such as RAID arrays, network attached storage (NAS) systems and storage area network (SAN) systems that provide efficient and reliable access to large volumes of data. In the 21st century, HDD usage expanded into consumer applications such as camcorders, cellphones, digital audio players, digital video players (e.g. the iPod Classic), digital video recorders, personal digital assistants and video game consoles.

HD heads are kept from contacting the platter surface by the air that is extremely close to the platter; that air moves at, or close to, the platter speed.[citation needed] The record and playback head are mounted on a block called a slider, and the surface next to the platter is shaped to keep it just barely out of contact. It's a type of air bearing.
The magnetic surface of each platter is conceptually divided into many small sub-micrometre-sized magnetic regions, each of which is used to encode a single binary unit of information. In today's HDDs, each of these magnetic regions is composed of a few hundred magnetic grains. Each magnetic region forms a magnetic dipole which generates a highly localized magnetic field nearby. The write head magnetizes a region by generating a strong local magnetic field. Early HDDs used an electromagnet both to generate this field and to read the data by using electromagnetic induction. Later versions of inductive heads included metal in Gap (MIG) heads and thin film heads. In today's heads, the read and write elements are separate, but in close proximity, on the head portion of an actuator arm. The read element is typically magneto-resistive while the write element is typically thin-film inductive.
In modern drives, the small size of the magnetic regions creates the danger that their magnetic state might be lost because of thermal effects. To counter this, the platters are coated with two parallel magnetic layers, separated by a 3-atom-thick layer of the non-magnetic element ruthenium, and the two layers are magnetized in opposite orientation, thus reinforcing each other.
Another technology used to overcome thermal effects to allow greater recording densities is perpendicular recording, first shipped in 2005[6], as of 2007 the technology was used in many HDDs.

windows vista

Windows Vista is a line of operating systems developed by Microsoft for use on personal computers, including home and business desktops, laptops, Tablet PCs, and media center PCs. Prior to its announcement on July 22, 2005, Windows Vista was known by its codename "Longhorn". Development was completed on November 8, 2006; over the following three months it was released in stages to computer hardware and software manufacturers, business customers, and retail channels. On January 30, 2007, it was released worldwide, and was made available for purchase and download from Microsoft's website.The release of Windows Vista came more than five years after the introduction of its predecessor, Windows XP, the longest time span between successive releases of Microsoft Windows.
Windows Vista contains many changes and new features, including an updated graphical user interface and visual style dubbed Windows Aero, improved searching features, new multimedia creation tools such as Windows DVD Maker, and redesigned networking, audio, print, and display sub-systems. Vista also aims to increase the level of communication between machines on a home network, using peer-to-peer technology to simplify sharing files and digital media between computers and devices. Windows Vista includes version 3.0 of the .NET Framework, which aims to make it significantly easier for software developers to write applications than with the traditional Windows API.
Microsoft's primary stated objective with Windows Vista, however, has been to improve the state of security in the Windows operating system. One common criticism of Windows XP and its predecessors has been their commonly exploited security vulnerabilities and overall susceptibility to malware, viruses and buffer overflows. In light of this, Microsoft chairman Bill Gates announced in early 2002 a company-wide "Trustworthy Computing initiative" which aims to incorporate security work into every aspect of software development at the company. Microsoft stated that it prioritized improving the security of Windows XP and Windows Server 2003 above finishing Windows Vista, thus delaying its completion.
While these new features and security improvements have garnered positive reviews, Vista has also been the target of much criticism and negative press. Criticism of Windows Vista has targeted its high system requirements, its more restrictive licensing terms, the inclusion of a number of new digital rights management technologies aimed at restricting the copying of protected digital media, lack of compatibility with some pre-Vista hardware and software, and the number of authorization prompts for User Account Control. As a result of these and other issues, Windows Vista has seen adoption and satisfaction rates lower than Windows XP.However Vista is keeping well up with expectations stated by Microsoft before its launch of getting 200 million users by January 2009.

Demographics of the United States

The United States is an urbanized nation, with 80.8% of its population of 305,186,613[1] residing in cities and suburbs as of mid-year 2005.[2] The mean population center of the United States has consistently shifted westward and southward, with California and Texas currently the most populous states. U.S. population growth is among the highest in developed countries, although its annual rate of 0.88% is below the world average annual rate of 1.16%.The total fertility rate in the United States estimated for 2008 is 2.1, which is roughly the replacement level for industrialized countries. However, the U.S. Census bureau states that the population is projected to reach 439 million in 2050,which is a 44% increase from 2008 compared to the UN projection of a world population increase of 37% for the same period. Children (people under age 18) made up a quarter of the U.S. population (24.6%), and people over age 65 one-eighth (12.7%) in 2006.

Population growth
The first U.S. census, in 1790, recorded four million Americans. By 2000, this number had grown to over 281 million. It is expected to reach 308 million by 2010 and 439 million by 2050.

U.S. population clock hits the 300 million mark

US population reaches 300 million
The total U.S. population crossed the 100 million mark around 1915, the 200 million mark in 1967, and the 300 million mark in 2006 (estimated on Tuesday, October 17).[6][7] The U.S. population more than tripled during the 20th century — a growth rate of about 1.3% a year — from about 76 million in 1900 to 281 million in 2000. This is unlike most European countries, especially Germany, Russia, Italy and Greece, whose populations are slowly declining, and whose fertility rates are below replacement.
Population growth is fastest among minorities, and according to the United States Census Bureau's estimation for 2005, 45% of American children under the age of 5 are minorities.[8] In 2007, the nation's minority population reached 102.5 million.[9] A year before, the minority population totaled 100.7 million. Hispanic and Latino Americans accounted for almost half (1.4 million) of the national population growth of 2.9 million between July 1, 2005, and July 1, 2006.

Based on a population clock maintained by the U.S. Census Bureau, the current U.S. population, as of 2:30 GMT (EST+5) October 22, 2008 is 305,468,880.A 2004 U.S. Census Bureau report predicted an increase of one third by the year 2050.A subsequent 2008 report projects a population of 439 million, which is a 44% increase from 2008.
As of November 2008 the US comprises approximately 4.5% of the world's population.
Cities
United States metropolitan area and List of United States cities by population
The United States has dozens of major cities, including 11 of the 55 global cities of all types — with three "alpha" global cities: New York City, Los Angeles and Chicago.
The following table expresses the figures for the populations of the top ten cities and their metropolitan areas, as of July 1, 2006.

population control

Time taken for each billion people to be added to the world's population
In biology a population is the collection of inter-breeding organisms of a particular species; in sociology, a collection of human beings. A population shares a particular characteristic of interest, most often that of living in a given geographic area. In taxonomy population is a low-level taxonomic rank.
Human populations can be defined by any characteristics such as mortality, migration, family (marriage and divorce), public health, work and the labor force, and family planning. Various aspects of human behavior in populations are also studied in sociology, economics, and geography.
Study of populations is almost always governed by the laws of probability, and the conclusions of the studies may thus not always be applicable to some individuals. This odd factor may be reduced by statistical means, but such a generalization may be too vague to imply anything. Demography is used extensively in marketing, which relates to economic units, such as retailers, to potential customers. For example, a coffee shop that wants to sell to a younger audience looks at the demographics of an area to be able to appeal to this younger audience.

Population control
Main article: Population control
Population control is the practice of curtailing population increase, usually by reducing the birth rate. Surviving records from Ancient Greece document the first known examples of population control. These include the colonization movement, which saw Greek outposts being built across the Mediterranean and Black Sea basins to accommodate the excess population of individual states. Infanticide, including abortion, was encouraged in some Greek city states in order to keep population down.[6]
An important example of mandated population control is People's Republic of China's one-child policy, in which having more than one child is made extremely unattractive. This has led to allegations that practices like forced abortions, forced sterilization, and infanticide are used as a result of the policy. The country's sex ratio at birth of 112 boys to 100 girls may be evidence that the latter is often sex-selective. However, other countries without a one-child policy also have similar sex ratios but for different reasons[citation needed].
It is helpful to distinguish between fertility control as individual decision-making and population control as a governmental or state-level policy of regulating population growth. Fertility control may occur when individuals or couples or families take steps to decrease or to regulate the timing of their own child-bearing. In Ansley Coale's oft-cited formulation, three preconditions for a sustained decline in fertility are: (1) acceptance of calculated choice (as opposed to fate or chance or divine will) as a valid element in fertility, (2) perceived advantages from reduced fertility, and (3) knowledge and mastery of effective techniques of control.[7] In contrast to a society with natural fertility, a society that desires to limit fertility and has the means to do so may use those means to delay childbearing, space childbearing, or stop childbearing. Delaying sexual intercourse (or marriage), or the adoption of natural or artificial means of contraception are most often an individual or family decision, not a matter of a state policy or societal-wide sanctions. On the other hand, individuals who assume some sense of control over their own fertility can also accelerate the frequency or success of child-bearing through planning.
At the societal level, declining fertility is almost an inevitable result of growing secular education of women . However, the exercise of moderate to high levels of fertility control does not necessarily imply low fertility rates. Even among societies that exercise substantial fertility control, societies with an equal ability to exercise fertility control (to determine how many children to have and when to bear them) may display widely different levels of fertility (numbers of children borne) associated with individual and cultural preferences for the number of children or size of families.[8]
In contrast to fertility control, which is mainly an individual-level decision, governments may attempt to exercise population control by increasing access to means of contraception or by other population policies and programs.[9] The idea of "population control" as a governmental or societal-level regulation of population growth does not require "fertility control" in the sense that it has been defined above, since a state can affect the growth of a society's population even if that society practices little fertility control. It's also important to embrace policies favoring population increase as an aspect of population control, and not to assume that states want to control population only by limiting its growth. To stimulate population growth, governments may support not only immigration but also pronatalist policies such as tax benefits, financial awards, paid work leaves, and childcare to encourage the bearing of additional children.[10] Such policies have been pursued in recent years in France and Sweden, for example. With the same goal of increasing population growth, on occasion governments have sought to limit the use of abortion or modern means of birth control. An example was Romania's 1966 ban on access to contraception and abortion on demand.
In ecology, population control is on occasions considered to be done solely by predators, diseases, parasites, and environmental factors. At many times human effects on animal and plant populations are also considered. See also [1]. Migrations of animals may be seen as a natural way of population control, for the food on land is more abundant on some seasons. The area of the migrations' start is left to reproduce the food supply for large mass of animals next time around. See also immigration.

COMPUTER

A computer is a machine that manipulates data according to a list of instructions.
The first devices that resemble modern computers date to the mid-20th century (around 1940 - 1945), although the computer concept and various machines similar to computers existed earlier. Early electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers.[1] Modern computers are based on tiny integrated circuits and are millions to billions of times more capable while occupying a fraction of the space.[2] Today, simple computers may be made small enough to fit into a wristwatch and be powered from a watch battery. Personal computers, in various forms, are icons of the Information Age and are what most people think of as "a computer"; however, the most common form of computer in use today is the embedded computer. Embedded computers are small, simple devices that are used to control other devices — for example, they may be found in machines ranging from fighter aircraft to industrial robots, digital cameras, and children's toys.
The ability to store and execute lists of instructions called programs makes computers extremely versatile and distinguishes them from calculators. The Church–Turing thesis is a mathematical statement of this versatility: any computer with a certain minimum capability is, in principle, capable of performing the same tasks that any other computer can perform. Therefore, computers with capability and complexity ranging from that of a personal digital assistant to a supercomputer are all able to perform the same computational tasks given enough time and storage capacity.