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Emulator
From Wikipedia, the free encyclopedia
This article is about emulators in computer science. For a line of digital musical instruments, see E-mu Emulator. For other uses, see Emulation (disambiguation).
DOSBox emulates the command-line interface of DOS.
In computing, an emulator is hardware and/or software that duplicates (or emulates) the functions of a first computer system in a different second computer system, so that the behavior of the second system closely resembles the behavior of the first system. This focus on exact reproduction of external behavior is in contrast to some other forms of computer simulation, in which an abstract model of a system is being simulated. For example, a computer simulation of a hurricane or a chemical reaction is not emulation.

Emulation refers to the ability of a computer program or electronic device to emulate (imitate) another program or device. Many printers, for example, are designed to emulate Hewlett-Packard LaserJet printers because so much software is written for HP printers. If a non-HP printer emulates an HP printer, any software written for a real HP printer will also run in the non-HP printer emulation and produce equivalent printing.
A hardware emulator is an emulator which takes the form of a hardware device. Examples include the DOS-compatible card installed in some old-world Macintoshes like Centris 610 or Performa 630 that allowed them to run PC programs and FPGA-based hardware emulators.
In a theoretical sense, the Church-Turing thesis implies that any operating environment can be emulated within any other. However, in practice, it can be quite difficult, particularly when the exact behavior of the system to be emulated is not documented and has to be deduced through reverse engineering. It also says nothing about timing constraints; if the emulator does not perform as quickly as the original hardware, the emulated software may run much more slowly than it would have on the original hardware, possibly triggering time interrupts to alter performance.
Emulation in preservation
Emulation is a strategy in digital preservation to combat obsolescence. Emulation focuses on recreating an original computer environment, which can be time-consuming and difficult to achieve, but valuable because of its ability to maintain a closer connection to the authenticity of the digital object.[1]
Emulation addresses the original hardware and software environment of the digital object, and recreates it on a current machine.[2] The emulator allows the user to have access to any kind of application or operating system on a current platform, while the software runs as it did in its original environment.[3] Jeffery Rothenberg, an early proponent of emulation as a digital preservation strategy states, "the ideal approach would provide a single extensible, long-term solution that can be designed once and for all and applied uniformly, automatically, and in synchrony (for example, at every refresh cycle) to all types of documents and media".[4] He further states that this should not only apply to out of date systems, but also be upwardly mobile to future unknown systems.[5] Practically speaking, when a certain application is released in a new version, rather than address compatibility issues and migration for every digital object created in the previous version of that application, one could create an emulator for the application, allowing access to all of said digital objects.
[edit]Benefits
Emulators maintain the original look, feel, and behavior of the digital object, which is just as important as the digital data itself.[6]
Despite the original cost of developing an emulator, it may prove to be the more cost efficient solution over time.[7]
Reduces labor hours, because rather than continuing an ongoing task of continual data migration for every digital object, once the library of past and present operating systems and application software is established in an emulator, these same technologies are used for every document using those platforms.[3]
Many emulators have already been developed and released under GNU General Public License through the open source environment, allowing for wide scale collaboration.[8]
Emulators allow video games exclusive to one system to be played on another. For example, a PlayStation 2 exclusive video game could (in theory) be played on a PC or Xbox 360 using an emulator.
[edit]Obstacles
Intellectual property - Many technology vendors implemented non-standard features during program development in order to establish their niche in the market, while simultaneously applying ongoing upgrades to remain competitive. While this may have advanced the technology industry and increased vendor’s market share, it has left users lost in a preservation nightmare with little supporting documentation due to the proprietary nature of the hardware and software.[9]
Copyright laws are not yet in effect to address saving the documentation and specifications of proprietary software and hardware in an emulator module.[10]
[edit]Emulators in new media art
Because of its primary use of digital formats, new media art relies heavily on emulation as a preservation strategy. Artists such as Cory Arcangel specialize in resurrecting obsolete technologies in their artwork and recognize the importance of a decentralized and deinstitutionalized process for the preservation of digital culture.
In many cases, the goal of emulation in new media art is to preserve a digital medium so that it can be saved indefinitely and reproduced without error, so that there is no reliance on hardware that ages and becomes obsolete. The paradox is that the emulation and the emulator have to be made to work on future computersTypes of emulators
Windows XP running an Acorn Archimedes emulator, which is in turn running a Sinclair ZX Spectrum emulator.
Most emulators just emulate a hardware architecture—if operating system firmware or software is required for the desired software, it must be provided as well (and may itself be emulated). Both the OS and the software will then be interpreted by the emulator, rather than being run by native hardware. Apart from this interpreter for the emulated binary machine's language, some other hardware (such as input or output devices) must be provided in virtual form as well; for example, if writing to a specific memory location should influence what is displayed on the screen, then this would need to be emulated.
While emulation could, if taken to the extreme, go down to the atomic level, basing its output on a simulation of the actual circuitry from a virtual power source, this would be a highly unusual solution. Emulators typically stop at a simulation of the documented hardware specifications and digital logic. Sufficient emulation of some hardware platforms requires extreme accuracy, down to the level of individual clock cycles, undocumented features, unpredictable analog elements, and implementation bugs. This is particularly the case with classic home computers such as the Commodore 64, whose software often depends on highly sophisticated low-level programming tricks invented by game programmers and the demoscene.
In contrast, some other platforms have had very little use of direct hardware addressing. In these cases, a simple compatibility layer may suffice. This translates system calls for the emulated system into system calls for the host system e.g., the Linux compatibility layer used on *BSD to run closed source Linux native software on FreeBSD, NetBSD and OpenBSD.
Developers of software for embedded systems or video game consoles often design their software on especially accurate emulators called simulators before trying it on the real hardware. This is so that software can be produced and tested before the final hardware exists in large quantities, so that it can be tested without taking the time to copy the program to be debugged at a low level and without introducing the side effects of a debugger. In many cases, the simulator is actually produced by the company providing the hardware, which theoretically increases its accuracy.
Math coprocessor emulators allow programs compiled with math instructions to run on machines that don't have the coprocessor installed, but the extra work done by the CPU may slow the system down. If a math coprocessor isn't installed or present on the CPU, when the CPU executes any coprocessor instruction it will make a determined interrupt (coprocessor not available), calling the math emulator routines. When the instruction is successfully emulated, the program continues executing.
Video game console emulators

Main article: Video game console emulator
Video game console emulators are programs that allow a computer or modern console to emulate a video game console. They are most often used to play older video games on personal computers and modern video game consoles, but they are also used to translate games into other languages, to modify existing games, and in the development process of home brew demos and new games for older systems. The internet has helped in the spread of console emulators, as most - if not all - would be unavailable for sale in retail outlets. Examples of console emulators that have been released in the last 2 decades are: Dolphin, Zsnes, Kega Fusion, Desmume, Epsxe, Project64, Visual Boy Advance, NullDC and Nestopia.