The United States of America
The United States of America is the 4th largest country in the world (after Russia, Canada and China). The total area of the country is about nine and a half million square kilometers.
If we look at the map of the USA we can see lowlands and mountains. The highest mountains are the Rocky Mountains, the Cordillera and the Sierra Nevada. America’s largest rivers are the Mississippi, the Missouri, the Rio Grande and the Columbia. The Great Lakes on the border with Canada are the largest and the deepest in the USA.
The climate is different in different parts of the country. The coldest regions are in the North. The climate of Alaska is artic; the climate of the central part is continental; the south has subtropical climate. Hot winds blowing from the Gulf of Mexico often bring typhoons.
The beginning of the country’s history runs back to the 17th century, when European settlers started occupying the territory of the modern USA. European countries – England, Spain, France, Holland – were fighting for the influence in the North America, but in 1776 the country won independence. July the 4th – the day of the US independence is celebrated as a symbol of human right fight.
The next important period of the US history was the Civil war between the North and the South. It began in 1861 and was a result of the contradictions between the slave-owning South and industrially developed North. In 1865 the Southern Army capitulated, slavery ended and the American way of development started.
The present day USA is a highly developed industrial country. It is one of the world’s leading producers of copper and oil and the world’s second producer of iron ore and coal. Among the most important industries are aircraft, cars, textiles, radio and television sets, armaments and others.
The population of the USA is about 250 million: people from dozens of nations live in 50 States. The USA is often called the country of immigrants.
The largest cities of the USA are New York, Los Angeles, Chicago, Philadelphia, Detroit, San Francisco and Washington. Washington, the capital of the USA, got its name after the name of its founder – the first American president. It is situated in the District of Columbia, the district with its own laws and regulations. Washington is often called the heart of America.
The USA is a federal Union of 50 States; each of them has its own governmental administration. The seat of the federal government is Washington D.C. According to the constitution, the government is divided into three branches: the executive, headed by the president, the legislative, exercised by the Congress and judicial, controlled by the Supreme Court. The congress consists of the Senate and the House of Representatives. There are two main political parties in the USA: the Republican and the Democratic ones.
Computers
The history of attempts to simplify the process of calculating began long before the Common Era. Romans used special calculating tables called abacus. Since the middle of the second millennium people have been trying to design a mechanical device for the processes of subtraction, addition, multiplication and division. One of the first devices was invented by Pascal in 1642. In 1830 an English scientist Charles Babbage developed an idea of a mechanical computer, but the technology of that time could not provide all necessary parts to complete a machine.
The first reliable computer was built in 1930. It was called differential analyzer and could solve differential equations.
One of the scientists, who greatly contributed to the development of a computer, was John von Neumann. He proposed the programs to be coded in numbers and stored in computer memory.
The invention of the transistor in 1947 resulted in the production of faster and more reliable electronic computers.
Now computers are much smaller and faster than their ancestors. According to the job they perform they are divided into two groups – general-purpose computers and special purpose computers. General purpose computers are not restricted to one user, but special purpose computers are designed to do one specific job.
According the principle of their work computers are classified into three different types: digital, analogue and hybrid computers. Digital computers process information by counting, comparing and rearranging digits in arithmetic/logic unit. All the data whether in the form of numbers, letters or symbols are represented by digits of the binary system. Analogue computers use physical analogs of numerical measurements; in other words, they solve problems by measuring the quantity of terms of another quantity. Hybrid computers combine the features of analogue and digital ones. They are as fast as analogue and as accurate as digital computers.