Architecture (562409), страница 11
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The application program requests a copy of any information the user enters by making a call to a system routine. The operating system converts any data so entered into a standard internal form. The application then uses this information to decide what to do next—for example, perform some desired processing function such as reformatting a page of text, or obtain some additional information from another file on a disk. In either case, calls to other system routines are used to actually carry out the display of the results or the accessing of the file from the disk.
When the application reaches completion or is prompted to quit, it makes further system calls to make sure that all data that needs to be saved has been written back to disk. It then makes a final system call to the operating system indicating that it is finished. The operating system then frees up the RAM and any devices that the application was using and awaits a command from the user to start another program.
| V | HISTORY |
People have been storing sequences of instructions in the form of a program for several centuries. Music boxes of the 18th century and player pianos of the late 19th and early 20th centuries played musical programs stored as series of metal pins, or holes in paper, with each line (of pins or holes) representing when a note was to be played, and the pin or hole indicating what note was to be played at that time. More elaborate control of physical devices became common in the early 1800s with French inventor Joseph Marie Jacquard’s invention of the punch-card controlled weaving loom. In the process of weaving a particular pattern, various parts of the loom had to be mechanically positioned. To automate this process, Jacquard used a single paper card to represent each positioning of the loom, with holes in the card to indicate which loom actions should be done. An entire tapestry could be encoded onto a deck of such cards, with the same deck yielding the same tapestry design each time it was used. Programs of over 24,000 cards were developed and used.
The world’s first programmable machine was designed—although never fully built—by the English mathematician and inventor, Charles Babbage. This machine, called the Analytical Engine, used punch cards similar to those used in the Jacquard loom to select the specific arithmetic operation to apply at each step. Inserting a different set of cards changed the computations the machine performed. This machine had counterparts for almost everything found in modern computers, although it was mechanical rather than electrical. Construction of the Analytical Engine was never completed because the technology required to build it did not exist at the time.
The first card deck programs for the Analytical Engine were developed by British mathematician Countess Augusta Ada Lovelace, daughter of the poet Lord Byron. For this reason she is recognized as the world’s first programmer.
The modern concept of an internally stored computer program was first proposed by Hungarian-American mathematician John von Neumann in 1945. Von Neumann’s idea was to use the computer’s memory to store the program as well as the data. In this way, programs can be viewed as data and can be processed like data by other programs. This idea greatly simplifies the role of program storage and execution in computers.
| VI | THE FUTURE |
The field of computer science has grown rapidly since the 1950s due to the increase in their use. Computer programs have undergone many changes during this time in response to user need and advances in technology. Newer ideas in computing such as parallel computing, distributed computing, and artificial intelligence, have radically altered the traditional concepts that once determined program form and function.
Computer scientists working in the field of parallel computing, in which multiple CPUs cooperate on the same problem at the same time, have introduced a number of new program models . In parallel computing parts of a problem are worked on simultaneously by different processors, and this speeds up the solution of the problem. Many challenges face scientists and engineers who design programs for parallel processing computers, because of the extreme complexity of the systems and the difficulty involved in making them operate as effectively as possible.
Another type of parallel computing called distributed computing uses CPUs from many interconnected computers to solve problems. Often the computers used to process information in a distributed computing application are connected over the Internet. Internet applications are becoming a particularly useful form of distributed computing, especially with programming languages such as Java . In such applications, a user logs onto a Web site and downloads a Java program onto their computer. When the Java program is run, it communicates with other programs at its home web site, and may also communicate with other programs running on different computers or web sites.
Research into artificial intelligence (AI) has led to several other new styles of programming. Logic programs, for example, do not consist of individual instructions for the computer to follow blindly, but instead consist of sets of rules: if x happens then do y. A special program called an inference engine uses these rules to “reason” its way to a conclusion when presented with a new problem. Applications of logic programs include automatic monitoring of complex systems, and proving mathematical theorems.
A radically different approach to computing in which there is no program in the conventional sense is called a neural network. A neural network is a group of highly interconnected simple processing elements, designed to mimic the brain. Instead of having a program direct the information processing in the way that a traditional computer does, a neural network processes information depending upon the way that its processing elements are connected. Programming a neural network is accomplished by presenting it with known patterns of input and output data and adjusting the relative importance of the interconnections between the processing elements until the desired pattern matching is accomplished. Neural networks are usually simulated on traditional computers, but unlike traditional computer programs, neural networks are able to learn from their experience.
Debugger
Debugger, in computer science, a program designed to help in debugging another program by allowing the programmer to step through the program, examine data, and check conditions. There are two basic types of debuggers: machine-level and source-level. Machine-level debuggers display the actual machine instructions (disassembled into assembly language) and allow the programmer to look at registers and memory locations. Source-level debuggers let the programmer look at the original source code (C or Pascal, for example), examine variables and data structures by name, and so on.
Electronic Games
| I | INTRODUCTION |
Electronic Games, software programs played for entertainment, challenge, or educational purposes. Electronic games are full of color, sound, realistic movement, and visual effects, and some even employ human actors. There are two broad classes of electronic games: video games, which are designed for specific video-game systems, handheld devices, and coin-operated arcade consoles; and computer games, which are played on personal computers.
Categories of electronic games include strategy games, sports games, adventure and exploration games, solitaire and multiplayer card games, puzzle games, fast-action arcade games, flying simulations, and versions of classic board games. Software programs that employ game-play elements to teach reading, writing, problem solving, and other basic skills are commonly referred to as edutainment.
Electronic games put to use a variety of skills. Many games, such as Tetris and Pac-Man, serve as tests of hand-eye coordination. In these games the challenge is to play as long as possible while the game gets faster or more complex. Other games, such as Super Mario Bros., are more sophisticated. They employ hand-eye coordination by challenging the player to react quickly to action on the screen, but they also test judgment and perseverance, sometimes by presenting puzzles that players must solve to move forward in the game. Strategy games ask players to make more complicated decisions that can influence the long-range course of the game. Electronic games can pit players against each other on the same terminal, across a local network, or via the Internet. Most games that require an opponent can also be played alone, however, with the computer taking on the role of opponent.
| II | VIDEO GAMES |
Video-game consoles, small handheld game devices, and coin-operated arcade games are special computers built exclusively for playing games. To control the games, players can use joysticks, trackballs, buttons, steering wheels (for car-racing games), light guns, or specially designed controllers that include a joystick, direction pad, and several buttons or triggers. Goggles and other kinds of virtual reality headgear can provide three-dimensional effects in specialized games. These games attempt to give the player the experience of actually being in a jungle, the cockpit of an airplane, or another setting or situation.
The first video games, which consisted of little more than a few electronic circuits in a simplified computer, appeared around 1970 as coin-operated cabinet games in taverns and pinball arcade parlors. In 1972 the Atari company introduced a game called Pong, based on table tennis. In Pong, a ball and paddles are represented by lights on the screen; the ball is set in motion, and by blocking it with the paddles, players knock it back and forth across the screen until someone misses. Pong soon became the first successful commercial video game. Arcade games have remained popular ever since.
Also in 1972 the Magnavox company introduced a home video-game machine called the Odyssey system. It used similar ball-and-paddle games in cartridge form, playable on a machine hooked up to a television. In 1977 Atari announced the release of its own home video-game machine, the Atari 2600. Many of the games played on the Atari system had originally been introduced as arcade games. The most famous included Space Invaders and Asteroids. In Space Invaders, a player has to shoot down ranks of aliens as they march down the screen. In Asteroids, a player needs to destroy asteroids before they crash into the player’s ship. The longer the player survives, the more difficult both games become. After Atari’s success with home versions of such games, other companies began to compete for shares of the fast-growing home video-game market. Major competitors included Coleco with its ColecoVision system, and Mattel with Intellivision. Some companies, particularly Activision, gained success solely by producing games for other companies’ video-game systems.
After several years of enormous growth, the home video-game business collapsed in 1983. The large number of games on offer confused consumers, and many video-game users were increasingly disappointed with the games they purchased. They soon stopped buying games altogether. Failing to see the danger the industry faced, the leading companies continued to spend millions of dollars for product development and advertising. Eventually, these companies ran out of money and left the video-game business.
Despite the decline in the home video-game business, the arcade segment of the industry continued to thrive. Pac-Man, which appeared in arcades in 1980, was one of the major sensations of the time. In this game, players maneuver a button-shaped character notched with a large mouth around a maze full of little dots. The goal is to gobble up all the dots without being touched by one of four enemies in hot pursuit. Another popular game was Frogger, in which players try to guide a frog safely across a series of obstacles, including a busy road.
In the mid-1980s, Nintendo, a Japanese company, introduced the Nintendo Entertainment System (NES). The NES touched off a new boom in home video games, due primarily to two game series: Super Mario Bros. and The Legend of Zelda. These and other games offered more advanced graphics and animation than earlier home video-game systems had, reengaging the interest of game players. Once again, other companies joined the growing home video-game market. One of the most successful was Sega, also headquartered in Japan. In the early 1990s, the rival video-game machines were Nintendo’s Super NES and Sega’s Genesis. These systems had impressive capabilities to produce realistic graphics, sound, and animation.
Throughout the 1990s Nintendo and Sega competed for dominance of the American home video-game market, and in 1995 another Japanese company, Sony, emerged as a strong competitor. Sega and Sony introduced new systems in 1995, the Sega Saturn and the Sony PlayStation. Both use games that come on CD-ROMs (compact discs). A year later, Nintendo met the challenge with the cartridge-based Nintendo 64 system, which has even greater processing power than its competitors, meaning that faster and more complex games can be created. In 1998 Sega withdrew the Saturn system from the U.S. market because of low sales.
| III | COMPUTER GAMES |
While video-game systems are used solely for gaming, games are only one of the many uses for computers. In computer games, players can use a keyboard to type in commands or a mouse to move a cursor around the screen, and sometimes they use both. Many computer games also allow the use of a joystick or game controller.
Computer games were born in the mid-1970s, when computer scientists started to create text adventure games to be played over networks of computers at universities and research institutions. These games challenged players to reach a goal or perform a certain task, such as finding a magical jewel. At each stop along the way, the games described a situation and required the player to respond by typing in an action. Each action introduced a new situation to which the player had to react. One of the earliest such games was called Zork.
Beginning in the late 1970s, Zork and similar games were adapted for use on personal computers, which were just gaining popularity. As technology improved, programmers began to incorporate graphics into adventure games. Because relatively few people owned home computers, however, the market for computer games grew slowly until the mid-1980s. Then, more dynamic games such as Choplifter, a helicopter-adventure game produced by Broderbund, helped fuel rising sales of computers. In 1982 Microsoft Corporation released Flight Simulator, which allows players to mimic the experience of flying an airplane.
As the power of personal computers increased in the 1980s, more sophisticated games were developed. Some of the companies that produced the most popular games were Sierra On-Line, Electronic Arts, and Strategic Simulations, Inc. (SSI). A line of so-called Sim games, produced by Maxis, enabled players to create and manage cities (SimCity), biological systems (SimEarth), and other organizational structures. In the process, players learned about the relationships between the elements of the system. For example, in SimCity a player might increase the tax rate to raise money only to find that people move out of the city, thus decreasing the number of taxpayers and possibly offsetting the increase in revenue. An educational mystery game called Where in the World Is Carmen Sandiego?, by Broderbund, was introduced in the 1980s and aimed at children. The game tests players’ reasoning ability and general knowledge by requiring them to track down an elusive master criminal by compiling clues found around the world.
Computer games continued to gain popularity in the 1990s, with the introduction of more powerful and versatile personal computers and the growing use of computers in schools and homes. With the development of CD-ROM technology, games also integrated more graphics, sounds, and videos, making them more engaging for consumers. The most successful games of the 1990s included Doom (by Id Software) and Myst (by Broderbund). Doom is a violent action game in which the player is a marine charged with fighting evil creatures. In Myst, a player wanders through a fictional island world, attempting to solve puzzles and figure out clues. The game’s appeal comes from the process of exploration and discovery.
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