Central processing unit
A central processing unit called a central processor or main processor, is the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logic and input/output operations specified by the instructions. The computer industry has used the term "central processing unit" at least since the early 1960s. Traditionally, the term "CPU" refers to a processor, more to its processing unit and control unit, distinguishing these core elements of a computer from external components such as main memory and I/O circuitry; the form and implementation of CPUs have changed over the course of their history, but their fundamental operation remains unchanged. Principal components of a CPU include the arithmetic logic unit that performs arithmetic and logic operations, processor registers that supply operands to the ALU and store the results of ALU operations and a control unit that orchestrates the fetching and execution of instructions by directing the coordinated operations of the ALU, registers and other components.
Most modern CPUs are microprocessors, meaning they are contained on a single integrated circuit chip. An IC that contains a CPU may contain memory, peripheral interfaces, other components of a computer; some computers employ a multi-core processor, a single chip containing two or more CPUs called "cores". Array processors or vector processors have multiple processors that operate in parallel, with no unit considered central. There exists the concept of virtual CPUs which are an abstraction of dynamical aggregated computational resources. Early computers such as the ENIAC had to be physically rewired to perform different tasks, which caused these machines to be called "fixed-program computers". Since the term "CPU" is defined as a device for software execution, the earliest devices that could rightly be called CPUs came with the advent of the stored-program computer; the idea of a stored-program computer had been present in the design of J. Presper Eckert and John William Mauchly's ENIAC, but was omitted so that it could be finished sooner.
On June 30, 1945, before ENIAC was made, mathematician John von Neumann distributed the paper entitled First Draft of a Report on the EDVAC. It was the outline of a stored-program computer that would be completed in August 1949. EDVAC was designed to perform a certain number of instructions of various types; the programs written for EDVAC were to be stored in high-speed computer memory rather than specified by the physical wiring of the computer. This overcame a severe limitation of ENIAC, the considerable time and effort required to reconfigure the computer to perform a new task. With von Neumann's design, the program that EDVAC ran could be changed by changing the contents of the memory. EDVAC, was not the first stored-program computer. Early CPUs were custom designs used as part of a sometimes distinctive computer. However, this method of designing custom CPUs for a particular application has given way to the development of multi-purpose processors produced in large quantities; this standardization began in the era of discrete transistor mainframes and minicomputers and has accelerated with the popularization of the integrated circuit.
The IC has allowed complex CPUs to be designed and manufactured to tolerances on the order of nanometers. Both the miniaturization and standardization of CPUs have increased the presence of digital devices in modern life far beyond the limited application of dedicated computing machines. Modern microprocessors appear in electronic devices ranging from automobiles to cellphones, sometimes in toys. While von Neumann is most credited with the design of the stored-program computer because of his design of EDVAC, the design became known as the von Neumann architecture, others before him, such as Konrad Zuse, had suggested and implemented similar ideas; the so-called Harvard architecture of the Harvard Mark I, completed before EDVAC used a stored-program design using punched paper tape rather than electronic memory. The key difference between the von Neumann and Harvard architectures is that the latter separates the storage and treatment of CPU instructions and data, while the former uses the same memory space for both.
Most modern CPUs are von Neumann in design, but CPUs with the Harvard architecture are seen as well in embedded applications. Relays and vacuum tubes were used as switching elements; the overall speed of a system is dependent on the speed of the switches. Tube computers like EDVAC tended to average eight hours between failures, whereas relay computers like the Harvard Mark I failed rarely. In the end, tube-based CPUs became dominant because the significant speed advantages afforded outweighed the reliability problems. Most of these early synchronous CPUs ran at low clock rates compared to modern microelectronic designs. Clock signal frequencies ranging from 100 kHz to 4 MHz were common at this time, limited by the speed of the switching de
A computing platform or digital platform is the environment in which a piece of software is executed. It may be the hardware or the operating system a web browser and associated application programming interfaces, or other underlying software, as long as the program code is executed with it. Computing platforms have different abstraction levels, including a computer architecture, an OS, or runtime libraries. A computing platform is the stage. A platform can be seen both as a constraint on the software development process, in that different platforms provide different functionality and restrictions. For example, an OS may be a platform that abstracts the underlying differences in hardware and provides a generic command for saving files or accessing the network. Platforms may include: Hardware alone, in the case of small embedded systems. Embedded systems can access hardware directly, without an OS. A browser in the case of web-based software; the browser itself runs on a hardware+OS platform, but this is not relevant to software running within the browser.
An application, such as a spreadsheet or word processor, which hosts software written in an application-specific scripting language, such as an Excel macro. This can be extended to writing fully-fledged applications with the Microsoft Office suite as a platform. Software frameworks. Cloud computing and Platform as a Service. Extending the idea of a software framework, these allow application developers to build software out of components that are hosted not by the developer, but by the provider, with internet communication linking them together; the social networking sites Twitter and Facebook are considered development platforms. A virtual machine such as the Java virtual machine or. NET CLR. Applications are compiled into a format similar to machine code, known as bytecode, executed by the VM. A virtualized version of a complete system, including virtualized hardware, OS, storage; these allow, for instance, a typical Windows program to run on. Some architectures have multiple layers, with each layer acting as a platform to the one above it.
In general, a component only has to be adapted to the layer beneath it. For instance, a Java program has to be written to use the Java virtual machine and associated libraries as a platform but does not have to be adapted to run for the Windows, Linux or Macintosh OS platforms. However, the JVM, the layer beneath the application, does have to be built separately for each OS. AmigaOS, AmigaOS 4 FreeBSD, NetBSD, OpenBSD IBM i Linux Microsoft Windows OpenVMS Classic Mac OS macOS OS/2 Solaris Tru64 UNIX VM QNX z/OS Android Bada BlackBerry OS Firefox OS iOS Embedded Linux Palm OS Symbian Tizen WebOS LuneOS Windows Mobile Windows Phone Binary Runtime Environment for Wireless Cocoa Cocoa Touch Common Language Infrastructure Mono. NET Framework Silverlight Flash AIR GNU Java platform Java ME Java SE Java EE JavaFX JavaFX Mobile LiveCode Microsoft XNA Mozilla Prism, XUL and XULRunner Open Web Platform Oracle Database Qt SAP NetWeaver Shockwave Smartface Universal Windows Platform Windows Runtime Vexi Ordered from more common types to less common types: Commodity computing platforms Wintel, that is, Intel x86 or compatible personal computer hardware with Windows operating system Macintosh, custom Apple Inc. hardware and Classic Mac OS and macOS operating systems 68k-based PowerPC-based, now migrated to x86 ARM architecture based mobile devices iPhone smartphones and iPad tablet computers devices running iOS from Apple Gumstix or Raspberry Pi full function miniature computers with Linux Newton devices running the Newton OS from Apple x86 with Unix-like systems such as Linux or BSD variants CP/M computers based on the S-100 bus, maybe the earliest microcomputer platform Video game consoles, any variety 3DO Interactive Multiplayer, licensed to manufacturers Apple Pippin, a multimedia player platform for video game console development RISC processor based machines running Unix variants SPARC architecture computers running Solaris or illumos operating systems DEC Alpha cluster running OpenVMS or Tru64 UNIX Midrange computers with their custom operating systems, such as IBM OS/400 Mainframe computers with their custom operating systems, such as IBM z/OS Supercomputer architectures Cross-platform Platform virtualization Third platform Ryan Sarver: What is a platform
North America is a continent within the Northern Hemisphere and all within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the west and south by the Pacific Ocean, to the southeast by South America and the Caribbean Sea. North America covers an area of about 24,709,000 square kilometers, about 16.5% of the earth's land area and about 4.8% of its total surface. North America is the third largest continent by area, following Asia and Africa, the fourth by population after Asia and Europe. In 2013, its population was estimated at nearly 579 million people in 23 independent states, or about 7.5% of the world's population, if nearby islands are included. North America was reached by its first human populations during the last glacial period, via crossing the Bering land bridge 40,000 to 17,000 years ago; the so-called Paleo-Indian period is taken to have lasted until about 10,000 years ago. The Classic stage spans the 6th to 13th centuries.
The Pre-Columbian era ended in 1492, the transatlantic migrations—the arrival of European settlers during the Age of Discovery and the Early Modern period. Present-day cultural and ethnic patterns reflect interactions between European colonists, indigenous peoples, African slaves and their descendants. Owing to the European colonization of the Americas, most North Americans speak English, Spanish or French, their culture reflects Western traditions; the Americas are accepted as having been named after the Italian explorer Amerigo Vespucci by the German cartographers Martin Waldseemüller and Matthias Ringmann. Vespucci, who explored South America between 1497 and 1502, was the first European to suggest that the Americas were not the East Indies, but a different landmass unknown by Europeans. In 1507, Waldseemüller produced a world map, in which he placed the word "America" on the continent of South America, in the middle of what is today Brazil, he explained the rationale for the name in the accompanying book Cosmographiae Introductio:... ab Americo inventore... quasi Americi terram sive Americam.
For Waldseemüller, no one should object to the naming of the land after its discoverer. He used the Latinized version of Vespucci's name, but in its feminine form "America", following the examples of "Europa", "Asia" and "Africa". Other mapmakers extended the name America to the northern continent, In 1538, Gerard Mercator used America on his map of the world for all the Western Hemisphere; some argue that because the convention is to use the surname for naming discoveries, the derivation from "Amerigo Vespucci" could be put in question. In 1874, Thomas Belt proposed a derivation from the Amerrique mountains of Central America. Marcou corresponded with Augustus Le Plongeon, who wrote: "The name AMERICA or AMERRIQUE in the Mayan language means, a country of perpetually strong wind, or the Land of the Wind, and... the can mean... a spirit that breathes, life itself." The United Nations formally recognizes "North America" as comprising three areas: Northern America, Central America, The Caribbean.
This has been formally defined by the UN Statistics Division. The term North America maintains various definitions in accordance with context. In Canadian English, North America refers to the land mass as a whole consisting of Mexico, the United States, Canada, although it is ambiguous which other countries are included, is defined by context. In the United States of America, usage of the term may refer only to Canada and the US, sometimes includes Greenland and Mexico, as well as offshore islands. In France, Portugal, Romania and the countries of Latin America, the cognates of North America designate a subcontinent of the Americas comprising Canada, the United States, Mexico, Greenland, Saint Pierre et Miquelon, Bermuda. North America has been referred to by other names. Spanish North America was referred to as Northern America, this was the first official name given to Mexico. Geographically the North American continent has many subregions; these include cultural and geographic regions. Economic regions included those formed by trade blocs, such as the North American Trade Agreement bloc and Central American Trade Agreement.
Linguistically and culturally, the continent could be divided into Latin America. Anglo-America includes most of Northern America and Caribbean islands with English-speaking populations; the southern North American continent is composed of two regions. These are the Caribbean; the north of the continent maintains recognized regions as well. In contrast to the common definition of "North America", which encompasses the whole continent, the term "North America" is sometimes used to refer only to Mexico, the United States, Greenland; the term Northern America refers to the northern-most countries and territories of North America: the United States, Bermuda, St. Pierre and Miquelon and Greenland. Although the term does not refer to a unifie
A light gun is a pointing device for computers and a control device for arcade and video games shaped to resemble a pistol. In aviation and shipping, it can be a directional signal lamp. Modern screen-based light guns work by building an optical sensor into the gun, which receives its input from the light emitted by on-screen target; the first device of this type, the light pen, was used on the MIT Whirlwind computer. The light gun and its ancestor the light pen are now used as pointing devices due to the popularity of the mouse and changes in monitor display technology—conventional light guns work only with CRT monitors; the first light guns appeared following the development of light-sensing vacuum tubes. It was not long before the technology began appearing in arcade shooting games, beginning with the Seeburg Ray-O-Lite in 1936; these early light gun games, like modern laser tag, used small targets onto which a light-sensing tube was mounted. If the beam struck the target, a "hit" was scored.
These games evolved throughout subsequent decades, culminating in Sega's Periscope, the company's first successful game released in 1966, which required the player to target cardboard ships. Periscope was an early electro-mechanical game, the first arcade game to cost a quarter per play. Sega's 1969 game Missile featured electronic sound and a moving film strip to represent the targets on a projection screen, their 1972 game Killer Shark featured a mounted light gun that shot at targets whose movement and reactions were displayed using back image projection onto a screen. Nintendo released the Beam Gun in 1970 and the Laser Clay Shooting System in 1973, followed in 1974 by the arcade game Wild Gunman, which used video projection to display the target on the screen. In 1975, Sega released the early co-operative light gun shooters Bullet Mark; the video game light gun is modeled on a ballistic weapon and is used for targeting objects on a video screen. With force feedback, the light gun can simulate the recoil of the weapon.
The first gun for a home console was in fact a big rifle, the Magnavox Odyssey's Shooting Gallery, which looked lifelike and needed to be "cocked" after each shot. Light guns are popular in arcade games, but had not caught on as well in the home video game console market until after the Nintendo Entertainment System, Sega Master System, Mega Drive/Genesis, Super Nintendo Entertainment System systems and Atari XEGS. Many home'Pong' systems of the 1970s included a gun for shooting simple targets on screen. Nintendo's NES Zapper for the NES is the most popular example of the light gun, Duck Hunt its most popular game. Traditional light guns cannot be used on the newer LCD and plasma screens, have problems with projection screens. There are light guns for Sega Saturn, PlayStation and several other console and arcade systems. Recent light gun video games include Resident Evil: The Umbrella Chronicles, Time Crisis 4, Virtua Cop 3, The House of the Dead: Overkill. In 2007, Nintendo released the Wii Zapper for the Wii, a peripheral, a plastic shell that houses both the Wii Remote and nunchuk for gun-style video games.
While it does not contain any traditional light gun technology, the peripheral makes use of the Wii Remote's built-in infrared tracking system to shoot targets that correspond on-screen. Its name is a reference to the classic NES Zapper for the Nintendo Entertainment System. Sony have released attachments that house the PlayStation Move motion controller in the form of a pistol and rifle, the latter named the Sharp Shooter. Namco's GunCon 3 uses an infrared optical sensor system similar to the Wii Remote; the "light gun" is named because it uses light as its method of detecting where on screen the user is targeting. The name leads one to believe that the gun itself emits a beam of light, but in fact most light guns receive light through a photodiode in the gun barrel. There are two versions of this technique that are used, but the concept is the same: when the trigger of the gun is pulled, the screen is blanked out to black, the diode begins reception. All or part of the screen is painted white in a way that allows the computer to judge where the gun is pointing, based on when the diode detects light.
The user of the light gun notices little or nothing, because the period in which the screen is blank is only a fraction of a second. The first detection method, used by the Zapper, involves drawing each target sequentially in white light after the screen blacks out; the computer knows that if the diode detects light as it is drawing a square, the target at which the gun is pointed. The diode tells the computer whether or not the player hit something, for n objects, the sequence of the drawing of the targets tell the computer which target the player hit after 1 + ceil refreshes. A side effect of this is that on poorly designed games a player can point the gun at a light bulb or other bright light source, pull the trigger, cause the system to falsely detect a hit on the first target every time. Better games account for this either by detecting if all targets appear to match or by displaying a black screen and verifying that no targets match; the second method, used by the Super Nintendo Entertainment System's Super Scope and computer light pens, is more elaborate and more accurate.
The trick to this method lies in
An arcade game or coin-op game is a coin-operated entertainment machine installed in public businesses such as restaurants and amusement arcades. Most arcade games are video games, pinball machines, electro-mechanical games, redemption games or merchandisers. While exact dates are debated, the golden age of arcade video games is defined as a period beginning sometime in the late 1970s and ending sometime in the mid-1980s. Excluding a brief resurgence in the early 1990s, the arcade industry subsequently declined in the Western hemisphere as competing home video game consoles such as the Sony PlayStation and Microsoft Xbox increased in their graphics and game-play capability and decreased in cost; the first popular "arcade games" included early amusement-park midway games such as shooting galleries, ball-toss games, the earliest coin-operated machines, such as those that claimed to tell a person's fortune or that played mechanical music. The old Midways of 1920s-era amusement parks provided the inspiration and atmosphere for arcade games.
In the 1930s the first coin-operated pinball machines emerged. These early amusement machines differed from their electronic cousins in that they were made of wood, they lacked plungers or lit-up bonus surfaces on the playing field, used mechanical instead of electronic scoring-readouts. By around 1977 most pinball machines in production switched to using solid-state electronics both for operation and for scoring. In 1966 Sega introduced an electro-mechanical game called Periscope - an early submarine simulator and light gun shooter which used lights and plastic waves to simulate sinking ships from a submarine, it became an instant success in Japan and North America, where it was the first arcade game to cost a quarter per play, which would remain the standard price for arcade games for many years to come. In 1967 Taito released an electro-mechanical arcade game of their own, Crown Soccer Special, a two-player sports game that simulated association football, using various electronic components, including electronic versions of pinball flippers.
Sega produced gun games which resemble first-person shooter video games, but which were in fact electro-mechanical games that used rear image projection in a manner similar to the ancient zoetrope to produce moving animations on a screen. The first of these, the light-gun game Duck Hunt, appeared in 1969; that same year, Sega released an electro-mechanical arcade racing game, Grand Prix, which had a first-person view, electronic sound, a dashboard with a racing wheel and accelerator, a forward-scrolling road projected on a screen. Another Sega 1969 release, Missile, a shooter and vehicle-combat simulation, featured electronic sound and a moving film strip to represent the targets on a projection screen, it was the earliest known arcade game to feature a joystick with a fire button, which formed part of an early dual-control scheme, where two directional buttons are used to move the player's tank and a two-way joystick is used to shoot and steer the missile onto oncoming planes displayed on the screen.
In 1970 Midway released the game in North America as S. A. M. I.. In the same year, Sega released Jet Rocket, a combat flight-simulator featuring cockpit controls that could move the player aircraft around a landscape displayed on a screen and shoot missiles onto targets that explode when hit. In the course of the 1970s, following the release of Pong in 1972, electronic video-games replaced electro-mechanical arcade games. In 1972, Sega released an electro-mechanical game called Killer Shark, a first-person light-gun shooter known for appearing in the 1975 film Jaws. In 1974, Nintendo released Wild Gunman, a light-gun shooter that used full-motion video-projection from 16 mm film to display live-action cowboy opponents on the screen. One of the last successful electro-mechanical arcade games was F-1, a racing game developed by Namco and distributed by Atari in 1976; the 1978 video game Space Invaders, dealt a yet more powerful blow to the popularity of electro-mechanical games. In 1971 students at Stanford University set up the Galaxy Game, a coin-operated version of the video game Spacewar.
This ranks as the earliest known instance of a coin-operated video game. In the same year, Nolan Bushnell created the first mass-manufactured game, Computer Space, for Nutting Associates. In 1972, Atari was formed by Ted Dabney. Atari created the coin-operated video game industry with the game Pong, the first successful electronic ping pong video game. Pong proved to be popular, but imitators helped keep Atari from dominating the fledgling coin-operated video game market. Taito's Space Invaders, in 1978, proved to be the first blockbuster arcade video game, its success marked the beginning of the golden age of arcade video games. Video game arcades sprang up in shopping malls, small "corner arcades" appeared in restaurants, grocery stores and movie theaters all over the United States and other countries during the late 1970s and early 1980s. Space Invaders, Pac-Man, Battlezone and Bosconian were popular. By 1981, the arcade video game industry was worth US$8 billion. During the late 1970s and 1980s, chains such as Chuck E.
Cheese's, Ground Round and Busters, ShowBiz Pizza Place and Gatti's Pizza combined
Video game genre
A video game genre is a classification assigned to a video game based on its gameplay interaction rather than visual or narrative differences. A video game genre is defined by a set of gameplay challenges and are classified independently of their setting or game-world content, unlike other works of fiction such as films or books. For example, a shooter game is still a shooter game, regardless of when it takes place; as with nearly all varieties of genre classification, the matter of any individual video game's specific genre is open to personal interpretation. Moreover, each individual game may belong to several genres at once; the first attempt to classify different genres of video games was made by Chris Crawford in his book The Art of Computer Game Design in 1984. In this book, Crawford focused on the player's experience and activities required for gameplay. Here, he stated that "the state of computer game design is changing quickly. We would therefore expect the taxonomy presented to become obsolete or inadequate in a short time."
Since among other genres, the platformer and 3D shooter genres, which hardly existed at the time, have gained a lot of popularity. As hardware capabilities have increased, new genres have become possible, with examples being increased memory, the move from 2D to 3D, new peripherals and location. Though genres were just interesting for game studies in the 1980s, the business of video games expanded in the 1990s and both smaller and independent publishers had little chance of surviving; because of this, games settled more into set genres that larger publishers and retailers could use for marketing. Due to "direct and active participation" of the player, video game genres differ from literary and film genres. Though one could state that Space Invaders is a science-fiction video game, such a classification "ignores the differences and similarities which are to be found in the player's experience of the game." In contrast to the visual aesthetics of games, which can vary it is argued that it is interactivity characteristics that are common to all games.
Descriptive names of genres take into account the goals of the game, the protagonist and the perspective offered to the player. For example, a first-person shooter is a game, played from a first-person perspective and involves the practice of shooting; the term "subgenre" may be used to refer to a category within a genre to further specify the genre of the game under discussion. Whereas "shooter game" is a genre name, "first-person shooter" and "third-person shooter" are common subgenres of the shooter genre. Other examples of such prefixes are real-time, turn based, side-scrolling; the target audience, underlying theme or purpose of a game are sometimes used as a genre identifier, such as with "games for girls," games for cats,"Christian game" and "Serious game" respectively. However, because these terms do not indicate anything about the gameplay of a video game, these are not considered genres. Video game genres vary in specificity, with popular video game reviews using genre names varying from "action" to "baseball."
In this practice, basic themes and more fundamental characteristics are used alongside each other. A game may combine aspects of multiple genres in such a way that it becomes hard to classify under existing genres. For example, because Grand Theft Auto III combined shooting and roleplaying in an unusual way, it was hard to classify using existing terms. Since the term Grand Theft Auto clone has been used to describe games mechanically similar to Grand Theft Auto III; the term roguelike has been developed for games that share similarities with Rogue. Elements of the role-playing genre, which focuses on storytelling and character growth, have been implemented in many different genres of video games; this is because the addition of a story and character enhancement to an action, strategy or puzzle video game does not take away from its core gameplay, but adds an incentive other than survival to the experience. According to some analysts, the count of each broad genre in the best selling physical games worldwide is broken down as follows.
The most popular genres are Shooter, Role-playing and Sports, with Platformer and Racing having both declined in the last decade. Puzzle games have declined when measured by sales, however, on mobile, where the majority of games are free-to-play, this genre remains the most popular worldwide. List of video game genres
Shoot 'em up
Shoot'em up is a subgenre of the shooter genre of video games. There is no consensus as to; some restrict the definition to games featuring spacecraft and certain types of character movement. The genre's roots can be traced back to Spacewar!, one of the earliest computer games, developed in 1962. The shoot'em up genre was established by the hit arcade game Space Invaders, which popularised and set the general template for the genre in 1978, the genre was further developed by arcade hits such as Asteroids and Galaxian in 1979. Shoot'em ups were popular throughout early 1990s. In the mid-1990s, shoot'em ups became a niche genre based on design conventions established in the 1980s, catered to specialist enthusiasts in Japan. "Bullet hell" games are a subgenre that features overwhelming numbers of enemy projectiles in visually impressive formations. A "shoot'em up" known as a "shmup" or "STG", is a game in which the protagonist combats a large number of enemies by shooting at them while dodging their fire.
The controlling player must rely on reaction times to succeed. Beyond this, critics differ on which design elements constitute a shoot'em up; some restrict the genre to games using fixed or scrolling movement. Others widen the scope to include games featuring such protagonists as robots or humans on foot, as well as including games featuring "on-rails" and "run and gun" movement. Mark Wolf restricts the definition to games featuring multiple antagonists, calling games featuring one-on-one shooting "combat games". Critics described any game where the primary design element was shooting as a "shoot'em up", but shoot'em ups became a specific, inward-looking genre based on design conventions established in those shooting games of the 1980s. Shoot'em ups are a subgenre of shooter game, in turn a type of action game; these games are viewed from a top-down or side-view perspective, players must use ranged weapons to take action at a distance. The player's avatar is a vehicle under constant attack. Thus, the player's goal is to shoot as as possible at anything that moves or threatens them.
In some games, the player's character can withstand some damage. The main skills required in shoot'em ups are memorising enemy attack patterns; some games feature overwhelming numbers of enemy projectiles and the player has to memorise their patterns to survive. These games belong to one of the fastest-paced video game genres. Large numbers of enemy characters are featured; these enemies may behave in a certain way dependent on their type, or attack in formations that the player can learn to predict. The basic gameplay tends to be straightforward and many games offset this with boss battles and a variety of weapons. Shoot'em ups have realistic physics. Characters can change direction with no inertia, projectiles move in a straight line at constant speeds; the player's character can collect "power-ups" which may afford the character greater protection, an "extra life", or upgraded weaponry. Different weapons are suited to different enemies, but these games keep track of ammunition; as such, players tend to fire indiscriminately, their weapons only damage legitimate targets.
Shoot'em ups are categorized by design elements viewpoint and movement:Fixed shooters restrict the protagonist to a single axis of motion, enemies attack in a single direction, each level is contained within a single screen. Atari's Centipede is a hybrid, in that the player can move but that movement is constrained to a small area at the bottom of the screen, the game otherwise meets the fixed shooter definition. Tube shooters feature craft flying through an abstract tube, such as Gyruss. Rail shooters limit the player to moving around the screen. Examples include Space Harrier, Captain Skyhawk, Star Wars: Rebel Assault, Panzer Dragoon, Star Fox 64, Sin and Punishment. Light-Gun games that are "on-rails" are not in the shoot-em-up category but the FPS category, the term has been applied to scripted events in first-person shooters such as Call of Duty. Scrolling shooters include horizontal scrolling games. Vertically scrolling shooters: In a vertically scrolling shoot'em up, the action is viewed from above and scrolls up the screen.
Horizontally scrolling shooters: In a "horizontal shooter" or "side-scrolling shooter", the action is viewed side-on and scrolls horizontally. Isometrically scrolling shooters: A small number of scrolling shooters, such as Sega's Zaxxon, feature an isometric point of view. Multidirectional shooters feature 360 degree movement where the protagonist may rotate and move in any direction. Multidirectional shooters with one joystick for movement and one joystick for firing in any direction independent of movement are called "twin-stick shooters."Bullet hell is a shoot'em up in which the entire screen is almost fille