An emulator duplicates (provides an emulation of) the functions of one system
System
System is a set of interacting or interdependent entities, real or abstract, forming an integrated whole.The concept of an "integrated whole" can also be stated in terms of a system embodying a set of relationships which are differentiated from relationships of the set to other elements, and from relationships between an element of the se... using a different system, so that the second system behaves like (and appears to be) the first system. This focus on exact reproduction of external behavior is in contrast to some other forms of computer simulation
Computer simulation
A computer simulation, a computer model or a computational model is a computer program, or network of computers, that attempts to simulation an abstract model of a particular system.... , which can concern an abstract model of the system being simulated.
Computer programs are Instruction for a computer. A computer requires programs to function. Moreover, a computer program does not run unless its instructions are executed by a Central processing unit; however, a program may communicate an Algorithm#Formalization of algorithms to people without running.... or electronic device to imitate another program or device.
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An emulator duplicates (provides an emulation of) the functions of one system
System
System is a set of interacting or interdependent entities, real or abstract, forming an integrated whole.The concept of an "integrated whole" can also be stated in terms of a system embodying a set of relationships which are differentiated from relationships of the set to other elements, and from relationships between an element of the se... using a different system, so that the second system behaves like (and appears to be) the first system. This focus on exact reproduction of external behavior is in contrast to some other forms of computer simulation
Computer simulation
A computer simulation, a computer model or a computational model is a computer program, or network of computers, that attempts to simulation an abstract model of a particular system.... , which can concern an abstract model of the system being simulated.
Computer programs are Instruction for a computer. A computer requires programs to function. Moreover, a computer program does not run unless its instructions are executed by a Central processing unit; however, a program may communicate an Algorithm#Formalization of algorithms to people without running.... or electronic device to imitate another program or device. Many printers
Computer printer
File:Lexmark X5100 Series.jpgIn computing, a printer is a peripheral which produces a hard copy of documents stored in computer file form, usually on physical print media such as paper or Transparency .... , for example, are designed to emulate Hewlett-Packard
Hewlett-Packard
The Hewlett-Packard Company , commonly referred to as HP, is a technology corporation headquartered in Palo Alto, California, United States.... LaserJet
LaserJet
LaserJet is the brand name used by the American computer company Hewlett-Packard for their line of xerography laser printers.... printers because so much software is written for HP printers. By emulating an HP printer, a printer can work with any software written for a real HP printer. Emulation "tricks" the running software into believing that a device is really some other device.
A hardware emulator is an emulator which takes the form of a hardware device. Examples includes 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
Field-programmable gate array
A field-programmable gate array is a semiconductor device that can be configured by the customer or designer after manufacturing—hence the name "field-programmable".... -based hardware emulator
Hardware emulation
Hardware emulation is the process of imitating the behavior of one or more pieces of hardware with another piece of hardware, typically a special purpose emulation system.... s.
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
Reverse engineering
Reverse engineering is the process of discovering the technological principles of a device, object or system through analysis of its structure, function and operation.... . 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.
Digital preservation is the management of digital information over time. Preservation of digital information is widely considered to require more constant and ongoing attention than preservation of other media.... to combat obsolescence
Obsolescence
Obsolescence is the state of being which occurs when a person, object, or service is no longer wanted even though it may still be in good working order.... . Emulation focuses on recreating the original computer environment and can be time-consuming and difficult, but valuable because of its ability to maintain a closer connection to the authenticity of the digital object.
A personal computer is made up of computer hardware, multiple physical components onto which can be loaded into a multitude of software that perform the functions of the computer.... and software
Computer software
Computer software, or just software is a general term used to describe a collection of computer programs, Algorithm and Software documentation that perform some tasks on a computer system.... environment of the digital object, and recreates it on a current machine. The emulator allows the user to have access to any kind of application
Application software
Application software is any tool that functions and is operated by means of a computer, with the purpose of supporting or improving the software user 's work.... or operating system
Operating system
An operating system is an interface between hardware and applications; it is responsible for the management and coordination of activities and the sharing of the limited resources of the computer.... on a current platform, while the software
Computer software
Computer software, or just software is a general term used to describe a collection of computer programs, Algorithm and Software documentation that perform some tasks on a computer system.... thinks it is in its original environment. Jeffery Rothenberg, an early proponent of emulation as a digital preservation
Digital preservation
Digital preservation is the management of digital information over time. Preservation of digital information is widely considered to require more constant and ongoing attention than preservation of other media.... 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”. He further states that this should not only apply to out of date systems, but also be upwardly mobile to future unknown systems. Practically speaking, when a certain application is released in a new version, rather than address compatibility
Computer compatibility
A family of computer models is said to be compatible if certain software that runs on one of the models can also be run on all other models of the family.... issues and migration
Data migration
Data migration is the process of transferring data between computer storage types, formats, or computer systems. Data migration is usually performed programmatically to achieve an automated migration, freeing up human resources from tedious tasks.... for every digital object created in the previous version of that application
Application software
Application software is any tool that functions and is operated by means of a computer, with the purpose of supporting or improving the software user 's work.... , we could create one emulator for the application
Application software
Application software is any tool that functions and is operated by means of a computer, with the purpose of supporting or improving the software user 's work.... , 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.
Despite the original cost of developing an emulator, it may prove to be the more cost efficient solution over time.
Reduces labor hours, because rather than continuing an ongoing task of continual data migration
Data migration
Data migration is the process of transferring data between computer storage types, formats, or computer systems. Data migration is usually performed programmatically to achieve an automated migration, freeing up human resources from tedious tasks.... 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.
The GNU General Public License is a widely used free software license, originally written by Richard Stallman for the GNU project. The GPL is the most popular and well-known example of the type of strong copyleft license that requires derived works to be available under the same copyleft.... through the open source
Open source
Open source is an approach to design, development, and distribution offering practical accessibility to a product's source . Some consider open source as one of various possible design approaches, while others consider it a critical Strategy element of their business operations.... environment, allowing for wide scale collaboration.
Intellectual property are law property over creations of the mind, both artistic and commercial, and the corresponding fields of law. Under intellectual property law, owners are granted certain exclusive rights to a variety of intangible assets, such as musical, literary, and artistic works; ideas, discoveries and inventions; and words, phra... - Many technology vendors implemented non-standard features during program development in order to establish their niche in the market, while simultaneously implementing ongoing upgrades to remain competitive. While this may have advanced the technology industry and increased vendor’s market share
Market share
Market share, in strategic management and marketing, is the percentage or proportion of the total available market or market segment that is being serviced by a company.... , it has left users lost in a preservation nightmare with little supporting documentation due to the proprietary nature of the hardware and software.
Copyright is a form of intellectual property which gives the creator of an original work exclusive rights for a certain time period in relation to that work, including its publication, distribution and adaptation; after which time the work is said to enter the public domain.... laws are not yet in effect to address saving the documentation and specifications of proprietary software and hardware in an emulator module.
Emulators in new media art
Because of its primary use of digital formats, new media art
New media art
New media art is an art genre that encompasses artworks created with new media technology, including digital art, computer graphics, computer animation, virtual art, Internet art, interactive art technologies, computer robotics, and art as biotechnology.... relies heavily on emulation as a preservation strategy. Artists such as Cory Arcangel
Cory Arcangel
Cory Arcangel is a digital artist who lives and works in Brooklyn. His work is concerned with the relationship between technology and culture, and with media appropriation.... 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.
Types of emulators
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 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 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
Commodore 64
The Commodore 64 is an 8-bit home computer released by Commodore International in August, 1982, at a price of United States dollar595. Preceded by the Commodore VIC-20 and Commodore MAX Machine, the C64 features 64 kilobytes of Random-access memory with sound and graphics performance that were superior to IBM-compatible computers of tha... , whose software often depends on highly sophisticated low-level programming tricks invented by game programmers and the demoscene
Demoscene
The demoscene is a computer art subculture that specializes in producing Demo , which are non-interactive audio-visual presentations that run in Real-time computing on a computer.... .
In contrast, some other platforms have had very little use of direct hardware addressing. In these cases, a simple compatibility layer
Compatibility layer
A compatibility layer is a term that refers to components that allow for non-native support of components.In software engineering, a compatibility layer allows binaries for a foreign system to run on a host system.... 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.
An embedded system is a special-purpose computer system designed to perform one or a few dedicated functions, often with real-time computing constraints.... s or video game console
Video game console
A video game console is an game development that produces a video signal which can be used with a display device to display a video game. The term "video game console" is used to distinguish a machine designed for consumers to buy and use solely for playing video games from a personal computer, which has many other functions, or arcade machi... s often design their software on especially accurate emulators called simulators
Simulation
Simulation is the imitation of some real thing, state of affairs, or process. The act of simulating something generally entails representing certain key characteristics or behaviors of a selected physical or abstract system.... 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 without introducing the side effects of a debugger
Debugger
A debugger is a computer program that is used to test and debug other programs. The code to be examined might alternatively be running on an Instruction Set Simulator, a technique that allows great power in its ability to halt when specific conditions are encountered but which will typically be much slower than executing the code directly on... . In many cases, the simulator is actually produced by the company providing the hardware, which theoretically increases its accuracy.
Math coprocessor emulators allow to run programs compiled with math instruction support on machines that haven't the math coprocessor installed, but making the program and the system be slow. e.g. the Linux i387 emulator that can be compiled on the kernel, or some MS-DOS compilers like Turbo C and DJGPP that includes math emulator compiled on the program. Currently the math emulator isn't necessary, because all current computers have math instruction support. The method of emulate the coprocessor is the following:
If the math coprocessor isn't installed on the computer or on the CPU, when the CPU executes any coprocessor instruction it will make an determinated 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.
Memory subsystem
It is possible for the memory subsystem emulation to be reduced to simply an array of elements each sized like an emulated word; however, this model falls very quickly as soon as any location in the computer's logical memory does not match physical memory.
This clearly is the case whenever the emulated hardware allows for advanced memory
management (in which case, the MMU
Memory management unit
A memory management unit , sometimes called paged memory management unit , is a computer hardware component responsible for handling accesses to computer memory requested by the central processing unit .... logic can be embedded in the memory emulator, made a module of its own, or sometimes integrated into the CPU simulator).
Even if the emulated computer does not feature an MMU, though, there are usually other factors that break the equivalence between logical and physical memory: many (if not most) architecture offer memory-mapped I/O
Memory-mapped I/O
Memory-mapped I/O and port I/O are two complementary methods of performing input/output between the Central processing unit and peripheral devices in a computer.... ; even those that do not almost invariably have a block of logical memory mapped to ROM
Read-only memory
Read-only memory is a class of computer storage media used in computers and other electronic devices. Because data stored in ROM cannot be modified , it is mainly used to distribute firmware .... , which means that the memory-array module must be discarded if the read-only nature of ROM is to be emulated. Features such as bank switching
Bank switching
Bank switching was a technique common in 8-bit microcomputer systems, to increase the amount of addressable random-access memory and read-only memory without extending the address bus.... or segmentation
Memory segment
x86 memory segmentation refers to the implementation of memory segmentation on the x86 architecture. Memory is divided into portions that may be addressed by a single index register without changing a 16-bit segment selector.... may also complicate memory emulation.
As a result, most emulators implement at least two procedures for writing to and reading from logical memory, and it is these procedures' duty to map every access to the correct location of the correct object.
On a base-limit addressing system where memory from address 0 to address ROMSIZE-1 is read-only memory, while the rest is RAM, something along the line of the following procedures would be typical:
void WriteMemory(word Address, word Value)
word ReadMemory(word Address)
CPU simulator
The CPU simulator is often the most complicated part of an emulator. Many emulators are written using "pre-packaged" CPU simulators, in order to concentrate on good and efficient emulation of a specific machine.
The simplest form of a CPU simulator is an interpreter
Interpreter (computing)
In computer science, an interpreter normally means a computer program that execution , i.e. performs, instructions written in a programming language.... , which follows the execution flow of the emulated program code and, for every machine code instruction encountered, executes operations on the host processor that are semantically equivalent to the original instructions.
A variable is a symbol that stands for a value that may vary; the term usually occurs in opposition to constant, which is a symbol for a non-varying value, i.e.... to each register
Processor register
In computer architecture, a processor register is a small amount of Computer storage available on the CPU whose contents can be accessed more quickly than storage available elsewhere.... and flag
Flag (computing)
In computer programming, flag refers to one or more bits that are used to store a binary numeral system value or code that has an assigned meaning.... of the simulated CPU. The logic of the simulated CPU can then more or less be directly translated into software algorithms, creating a software re-implementation that basically mirrors the original hardware implementation.
The following example illustrates how CPU simulation can be accomplished by an interpreter. In this case, interrupts are checked-for before every instruction executed, though this behavior is rare in real emulators for performance reasons.
void Execute(void)
Interpreters are very popular as computer simulators, as they are much simpler to implement than more time-efficient alternative solutions, and their speed is more than adequate for emulating computers of more than roughly a decade ago on modern machines.
However, the speed penalty inherent in interpretation can be a problem when emulating computers whose processor speed is on the same order of magnitude
Order of magnitude
An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed Geometric progression to the class preceding it.... as the host machine. Until not many years ago, emulation in such situations was considered completely impractical by many.
What allowed breaking through this restriction were the advances in dynamic recompilation
Dynamic recompilation
In computer science, dynamic recompilation is a feature of some emulators and virtual machines, where the system may compile some part of a Computer program during execution.... techniques. Simple a priori translation of emulated program code into code runnable on the host architecture is usually impossible because of several reasons:
In computer science, self-modifying code is Code that alters its own Instruction while it is Execution - usually to reduce the instruction path length and improve performance.... , even if it is modified only by the emulated operating system when loading the code (for example from disk)
there may not be a way to reliably distinguish data
DATA
Debt, AIDS, Trade in Africa is a multinational Non-governmental organization founded in January 2002 in London by U2's Bono along with Robert Sargent Shriver III and activists from the Jubilee 2000 Drop the Debt campaign.... (which should not be translated) from executable
Executable
In computing, an executable causes a computer "to perform indicated tasks according to encoded instruction ," as opposed to a file that only contains data .... code
Code
In communications, a code is a Operator for converting a piece of information into another form or representation , not necessarily of the same type.... .
Various forms of dynamic recompilation, including the popular Just In Time compiler (JIT) technique, try to circumvent these problems by waiting until the processor control flow jumps into a location containing untranslated code, and only then ("just in time") translates a block of the code into host code that can be executed.
The translated code is kept in a code cache
Cache
In computer science, a cache is a collection of data duplicating original values stored elsewhere or computed earlier, where the original data is expensive to fetch or to compute, compared to the cost of reading the cache.... , and the original code is not lost or affected; this way, even data segments can be (meaninglessly) translated by the recompiler, resulting in no more than a waste of translation time.
Speed may not be desirable as some older games were not designed with the speed of faster computers in mind. A game designed for a 30 MHz PC with a level timer of 300 game seconds might only give the player 30 seconds on a 300 MHz PC. Other programs, such as some DOS programs, may not even run on faster computers.
I/O
Most emulators do not, as mentioned earlier, emulate the main system bus; each I/O device is thus often treated as a special case, and no consistent interface for virtual peripherals is provided.
This can result in a performance advantage, since each I/O module can be tailored to the characteristics of the emulated device; designs based on a standard, unified I/O API
Application programming interface
An application programming interface is a set of subroutine, data structures, class and/or Protocol provided by library and/or operating system Service s in order to support the building of applications.... can, however, rival such simpler models, if well thought-out, and they have the additional advantage of "automatically" providing a plug-in service through which third-party virtual devices can be used within the emulator.
A unified I/O API may not necessarily mirror the structure of the real hardware bus: bus design is limited by several electric constraints and a need for hardware concurrency management that can mostly be ignored in a software implementation.
Even in emulators that treat each device as a special case, there is usually a common basic infrastructure for:
In computing, an interrupt is an asynchronous communication signal from hardware indicating the need for attention or a synchronous event in software indicating the need for a change in execution.... s, by means of a procedure that sets flags readable by the CPU simulator whenever an interrupt is raised, allowing the virtual CPU to "poll for (virtual) interrupts"
writing to and reading from physical memory, by means of two procedures similar to the ones dealing with logical memory (although, contrary to the latter, the former can often be left out, and direct references to the memory array be employed instead)
Emulate or Simulate?
The word "emulator" was coined in 1957 at IBM, as an optional feature in the IBM 709
IBM 709
The IBM 709 was an early computer system introduced by International Business Machines in August, 1958. It was an improved version of the IBM 704 and the second member of the IBM 700/7000 series#Scientific Architecture of scientific computers.... to execute legacy IBM 704
IBM 704
The IBM 704, the first mass-produced computer with floating point arithmetic hardware, was introduced by IBM in April, 1954. The 704 was significantly improved over the IBM 701 in terms of architecture as well as implementation, and was not compatible with its predecessor.... programs on the IBM 709. Registers and frequently used 704 instructions were emulated in 709 hardware. Complex 704 instructions were simulated in 709 software. In 1963, IBM constructed emulators for development of the NPL (360) product line, for the "new combination of software, microcode, and hardware".
It has recently become common to use the word "emulate" in the context of software. However, before 1980, "emulation" referred only to hardware emulation, while "simulation" referred to software emulation. For example, a computer especially built for running programs designed for another architecture is an emulator. In contrast, a simulator could be a program which runs on a PC, so that old Atari games can be run on it. Purists continue to insist on this distinction, but currently the term "emulation" often means the complete imitation of a machine executing binary code.
Console emulators
Main article: Console emulator
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 homebrewed demos and new games for older systems.
A terminal emulator, terminal application, term, or tty for short, is a program that emulates a "dumb" video Computer terminal within some other display architecture....
Terminal emulators are software programs that provide modern computers and devices interactive access to applications running on mainframe computer
Mainframe computer
Mainframes are computers used mainly by large organizations for critical applications, typically bulk data processing such as census, industry and consumer statistics, Enterprise Resource Planning, and financial transaction processing.... operating systems or other host systems such as HP-UX
HP-UX
HP-UX 11i is Hewlett-Packard's proprietary software implementation of the Unix operating system, based on UNIX System V . It runs on the HP 9000 PA-RISC-based range of central processing unit and HP Integrity Intel's Itanium-based systems, and was also available for later Apollo/Domain systems.... or OpenVMS
OpenVMS
OpenVMS , previously known as VAX-11/VMS, VAX/VMS or VMS, is the name of a high-end computer server operating system that runs on the VAX and DEC Alpha families of computers, developed by Digital Equipment Corporation of Maynard, Massachusetts, Massachusetts , and most recently on Hewlett-Packard systems built around the In... . Terminals such as the IBM 3270
IBM 3270
The IBM 3270 is a class of computer terminal made by IBM since 1972 normally used to communicate with IBM mainframes. As such, it was the successor to the IBM 2260 display terminal.... or VT100
VT100
VT100 is a video computer terminal which was made by Digital Equipment Corporation . It became the de facto standard used by terminal emulators.... 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
Attachmate
Attachmate is a major software company owned by an investment group led by Francisco Partners, Golden Gate Capital, and Thoma Cressey Bravo. Attachmate focuses on host connectivity and systems and security management software.... , IBM Personal Communications
List of IBM products
The following is a list of products, some notable, some less so, from the International Business Machines Corporation and its predecessor corporations, beginning in the 1890s, and spanning punched card equipment, time clocks, and typewriters, via mainframe computers and minicomputers, to microprocessors, software, and more.... and Micro Focus Rumba.
A computer simulation, a computer model or a computational model is a computer program, or network of computers, that attempts to simulation an abstract model of a particular system.... is the larger field of modeling real-world phenomenon (e.g. physics and economy) using computers.
For rewriting a computer program into a different programming language or platform, see Porting
Porting
In computer science, porting is the process of adapting software so that an executable Computer program can be created for a computing environment that is different from the one for which it was originally designed .... .
A field-programmable gate array is a semiconductor device that can be configured by the customer or designer after manufacturing—hence the name "field-programmable".... (FPGAs)
Other uses of the term "emulator" in the field of computer science:
A terminal emulator, terminal application, term, or tty for short, is a program that emulates a "dumb" video Computer terminal within some other display architecture....
Logic simulation is the use of a computer program to simulate the operation of a digital circuit. Logic simulation is the primary tool used for verifying the logical correctness of a hardware design....
High-level emulation is an approach for construction of emulators that are used to develop software for new computers that have not yet been built, or to revive legacy software written for obsolete computers, especially for video game console systems....
In computing, binary translation is the emulation of one instruction set by another through translation of Machine language. Sequences of instruction s are translated from the source to the target instruction set....
An in-circuit emulator is a hardware device used to debugger the software of an embedded system. It is usually in the form of bond-out processor which has many internal signals brought out for the purpose of debugging.... (ICE)
MAME is an emulator application designed to recreate the hardware of arcade game systems in software, with the intent of preserving gaming history and preventing vintage games from being lost or forgotten....
Data migration is the process of transferring data between computer storage types, formats, or computer systems. Data migration is usually performed programmatically to achieve an automated migration, freeing up human resources from tedious tasks....
In technology, for example in telecommunications and computing, a device or technology is said to be backwards compatible if it allows input generated by older devices....
Forward compatibility is the ability of a system to gracefully accept input intended for later versions of itself.Although forward compatibility and extensibility are similar, they are not the same....
Keeping Emulation Environments Portable is a European project aiming to preserve digital heritage by emulating all platforms rather than continually converting data to newer formats....
External links
is a repertory of emulators and their respective histories.
