In computing, an emulator is hardware or software or both that duplicates (or emulates) the functions of a first computer system (the guest) in a different second computer system (the host), so that the emulated behavior closely resembles the behavior of the real system. This focus on exact reproduction of 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.
DOSBox emulates the command-line interface of DOS.
Emulators in computing
Basilisk II emulates a Macintosh 68k using interpretation code and dynamic recompilation.
Emulation refers to the ability of a computer program in an 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 that 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. 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. 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] 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 computers.[11] Emulation in future systems design Emulation technics are commonly used during the design and development of new systems. It eases the development process by making it allowing to detect, recreate and repair flaws in the design even before the system is actually built[12]. It is particularly useful in the design of multi-cores systems, where concurrency errors can be very difficult to detect and correct without the controlled environment provided by virtual hardware [13]. This also allows the software development to take place before the hardware is ready[14], thus helping to validate design decisions.
Types 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. Structure of an emulator Typically, an emulator is divided into modules that correspond roughly to the emulated computer's subsystems. Most often, an emulator will be composed of the following modules: • a CPU emulator or CPU simulator (the two terms are mostly interchangeable in this case) • a memory subsystem module • various I/O devices emulators Buses are often not emulated, either for reasons of performance or simplicity, and virtual peripherals communicate directly with the CPU or the memory subsystem.
Logic simulators Logic simulation is the use of a computer program to simulate the operation of a digital circuit such as a processor. This is done after a digital circuit has been designed in logic equations, but before the circuit is fabricated in hardware. Functional simulators Functional simulation is the use of a computer program to simulate the execution of a second computer program written in symbolic assembly language or compiler language, rather than in binary machine code. By using a functional simulator, programmers can execute and trace selected sections of source code to search for programming errors (bugs), without generating binary code. This is distinct from simulating execution of binary code, which is software emulation. The first functional simulator was written by Autonetics about 1960 for testing assembly language programs for later execution in military computer D-17B. This made it possible for flight programs to be written, executed, and tested before D-17B computer hardware had been built. Autonetics also programmed a functional simulator for testing flight programs for later execution in the military computer D-37C. Video game console emulators Video game console emulators are programs that allow a personal computer or video game console to emulate different video game console. They are most often used to play older video games on personal computers and 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. Terminal emulators Terminal emulators are software programs that provide modern computers and devices interactive access to applications running on mainframe computer operating systems or other host systems such as HP-UX or OpenVMS. Terminals such as the IBM 3270 or VT100 and many others, are no longer produced as physical devices. Instead, software running on modern operating systems simulates a "dumb" terminal and is able to render the graphical and text elements of the host application, send keystrokes and process commands using the appropriate terminal protocol. Some terminal emulation applications include Attachmate Reflection, IBM Personal Communications, AlphaVM virtual machine by EmuVM, Stromasys CHARON-VAX/AXP and Micro Focus Rumba. Please Leave Your Comments if this post helped you..... Regards Mz......
, otherwise dnno ,how much idiotic things i wud hav done... Gracias , once again... 