Simulator or Emulator What is the difference

Question

While I understand what simulation and emulation mean in general  I almost always get confused about them  Assume that I create a piece of software that mimics existing hardware software  what should I call it  A simulator or an emulator   Could anyone explain the difference in terms of programming   Bonus  What is the difference in English between these two terms   Sorry  I am not a native speaker

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An emulator is an alternative to the real system but a simulator is used to optimize  understand and estimate the real system

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If a flight-simulator could transport you from A to B then it would be a flight-emulator   An emulator can replace the original for real use  A Virtual PC emulates a PC     A simulator is a model for study and analysis     An emulator will always have to operate close to real-time  For a simulator that is not always the case  A geological simulation could do 1000 years second or more

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A Virtual PC tries to emulate a Computer  from the point of view of a Programmer BUT  at the same time  it simulates a Computer from the point of view of a Electrical Engineer

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Emulation is the process of mimicking the outwardly observable behavior to match an existing target   The internal state of the emulation mechanism does not have to accurately reflect the internal state of the target which it is emulating   Simulation  on the other hand  involves modeling the underlying state of the target   The end result of a good simulation is that the simulation model will emulate the target which it is simulating     Ideally  you should be able to look into the simulation and observe properties that you would also see if you looked into the original target   In practice  there may some shortcuts to the simulation for performance reasons -- that is  some internal aspects of the simulation may actually be an emulation   MAME is an arcade game emulator  Hyperterm is a  not very good  terminal emulator   There s no need to model the arcade machine or a terminal in detail to get the desired emulated behavior   Flight Simulator is a simulator  SPICE is an electronics simulator   They model as much as possible every detail of the target to represent what the target does in reality   EDIT  Other responses have pointed out that the goal of an emulation is to able to substitute for the object it is emulating   That s an important point   A simulation s focus is more on the modelling of the internal state of the target -- and the simulation does not necessarily lead to emulation   In particular  a simulation may run far slower than real time   SPICE  for example  cannot substitue for an actual electronics circuit  even if assuming there was some kind of magical device that perfectly interfaces electrical circuits to a SPICE simulation   A simulation  Simulation does not always lead to emulation --

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Both terms are something completely different and only intersect very little   To find the right term is actually very easy  just think about following  A simulation does not do anything for real   You can study it  for example how computer work  but it usually has no outcome other than that     A plane crash in a Flight Simulator causes no real harm   A weather forecast simulation itself does not change the weather  An emulation does something for real   You can work with an emulated computer like with a physical one and create documents with it   And a plane crash in a Flight Emulator would have an outcome  like people experiencing the real impact including possible physical harm  Your confusion probably stems from the fact  that  quot studying the simulation quot  and  quot accessing the emulation quot  often is quite the same thing  You are not alone with your confusion   The Film  quot Matrix quot  speaks of a simulation   However The Matrix is running an emulation  as it has real impact on all members of The Matrix   In contrast the training room has no real impact  so this is a simulation  of The Matrix   Let s see some examples  Simulated vs  Emulated Rain Take a water hose in the garden and let it rain   What s the difference between simulation and emulation here  When you are simulating rain  people still will blame you for getting wet   Your rain has some real impact on the world  but your simulation hasn t  as the simulation does not fool anybody in that it is real rain  In contrast  when you are emulating rain  people would blame the weather   This is  your emulated rain really behaves like rain in reality  This rain emulation hence distorts reality  in making people belie in the wrong culprit   It took me quite some time to understand that  Hence it isn t easy nor obvious which explains all the confusion   Keep in mind that a simulation can have sideeffects  like the weather forecast is based on simulations  which takes quite some computing power and thus electrical energy  which has an environmental impact  Hence in the example of  quot simulated rain quot   people getting wet just is a sideffect and not part of the simulation   Same is true if you simulate a rainbow with this simulated rain   While the property of  quot how rainbows work quot  is part of this simulation  the simulation itself is not providing the rainbow  this just happens due to refraction of the sun on the sideffect of the waterdrops  Simulated vs  Emulated Computer While you might think  quot a simulated computer can have an outcome quot  this is practically wrong reasoning   If you save files onto a simulated harddrive  these files cannot leave the simulated drive outside of the simulation   You can obtain the files by studying the simulated drive  but this is not part of the simulation itself  In case the harddrive saves the data such  that the data is actually usable outside of the simulation  you have an emulated harddrive within the simulation to do so  So an emulation can be part of a simulation and vice versa  Simulated vs  Emulated Filesystem If you simulate a filesystem  you probably  for practicability  will choose to save the files onto your real filesystem as-is  perhaps with some additional meta-information    In that case the simulation seems to create real  quot value quot  outside of the simulation   Usable files  But this is just by coincidence  because your simulated filesystem actually emulates a filesystem as well   You actually emulated the outside filesystem inside your simulation  Simulated vs  Emulated TPM or HSM A good example of the difference is  when you think of security   A TPM is a specific device to keep it s own keys secure  source of identity  while an HSM is a general device to secure foreign keys  verify identity    Fun Fact   My fingers constantly type TMP instead of TPM   If you simulate a TPM this has a huge effect on security  because then you can observe the internal states of the TPM   Which renders all the security void   Even that such a simulation can give you valuable hints of improving the design of a TPM itself  you won t want to expose precious data to the simulated TPM for real  However if you emulate a TPM you will try to hide these internal states to the outside as good as you can   Such an emulated TPM then can be possibly used to really secure something else better than without it  With a real TPM you cannot emulate the properties of a real HSM   All you can archive is to simulate an HSM  but this will not have the security properties of a real HSM  so all data which is stored in this simulated HSM will not be protected  they will only be protected within the simulation itself   In contrast  with a real HSM you can emulate a TPM with all properties of a real TPM   For this the HSM needs to be constructed such  that no information needs to leave the HSM which does not leave a TPM as well   Please note that I do not know anything about HSMs or TPMs in particular  so it might be that there are no HSMs out there which are able to provide emulated TPMs   Simulated vs  Emulated World If our world is simulated  we are simulations  too   Hence some spectator  let s call her God  can look at us and change the simulation any time   Also we cannot find out if we are simulated or not   As I am pretty sure that I know that I am  I do not think I am simulated  because self-awareness looks like an effect with a real component to me  which contradicts simulation   This also means  our world cannot be a simulation  too  as a simulation can only affect me like the world does  if I am part of the simulation  But our world still can be emulated  like in the Film  quot Matrix quot    as all I have to  quot prove the world quot  is my state of mind and sensory input  which I cannot verify  as I cannot leave myself   If I am not part of the emulation  then there should be a chance to observe discontinuity  like in the film  quot Matrix quot    in case the emulation does not work flawlessly  This changes when I emulated  too  like running an OS in an emulator   Then I cannot observe such errors  as my state can be reset from within the emulation  call it  Sleep  without observable discontinuation  However I rather think that the world is a holographic hallucination than something like an emulation   Because if it is emulated  then I am pwned by somebody  call him Rick  who is running the emulation for some purpose  while a hallucination is purely my own thing  I stop here  because hallucinations lead us to something completely different

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Simulation   For analysis and study  Emulation   For usage as a substitute  A simulator is an environment which models but an emulator is one that replicates the usage as on the original device or system   Simulator mimics the activity of something that it is simulating  It  appears  a lot can go with this  appears   depending on the context  to be the same as the thing being simulated  For example the flight simulator  appears  to be a real flight to the user  although it does not transport you from one place to another    Emulator  on the other hand  actually  does  what the thing being emulated does  and in doing so it too  appears to be doing the same thing   An emulator may use different set of protocols for mimicking the thing being emulated  but the result outcome is always the same as the original object  For example  EMU8086 emulates the 8086 microprocessor on your computer  which obviously is not running on 8086    different protocols   but the output it gives is what a real 8086 would give

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This question is probably best answered by taking a look at historical practice   In the past  I ve seen gaming console emulators on PC for the PlayStation  amp  SEGA   Simulators are commonplace when referring to software that tries to mimic real life actions  such as driving or flying  Gran Turismo and Microsoft Flight Simulator spring to mind as classic examples of simulators   As for the linguistic difference  emulation usually refers to the action of copying someone s  or something s  praiseworthy characteristics or behaviors  Emulation is distinct from imitation  in which a person is copied for the purpose of mockery   The linguistic meaning of the verb  simulation  is essentially to pretend or mimic someone or something

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In more or less normal parlance  If your software can do everything the mimicked system can do  it s an emulator  If it only approximates the results of a system  IT or otherwise   it s a simulator

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It s a difference in focus  Emulators1 focus on recreating the behavior of a system  with no regard for how the system functions internally  Simulators2 focus on modeling the components of a system  You use an emulator when you care mostly about what a system does  and a simulator when you care about how it does it   As for their general English meanings  emulation is  the endeavor to equal or to excel another in qualities or actions   while simulation is  to model  replicate  duplicate the behavior  appearance or properties of   Not much difference  Emulation comes from   mulus   striving  rivaling   and is related to  imitate  and  image   which suggests a surface-lever resemblance   Simulation  comes from similis  like   as does the word  similar   which perhaps suggests a deeper congruence   References    Wikipedia  Emulator Wikipedia  Computer Simulation Wiktionary  emulation Wiktionary  simulation Etymology Online  emulation Etymology Online  simulation

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To understand the difference between a simulator and an emulator  keep in mind that a simulator tries to mimic the behavior of a real device  For example  in the case of the iOS Simulator  it simulates the real behavior of an actual iPhone iPad device  However  the Simulator itself uses the various libraries installed on the Mac  such as QuickTime  to perform its rendering so that the effect looks the same as an actual iPhone  In addition  applications tested on the Simulator are compiled into x86 code  which is the byte-code understood by the Simulator  A real iPhone device  conversely  uses ARM-based code   In contrast  an emulator emulates the working of a real device  Applications tested on an emulator are compiled into the actual byte-code used by the real device  The emulator executes the application by translating the byte-code into a form that can be executed by the host computer running the emulator   To understand the subtle difference between simulation and emulation  imagine you are trying to convince a child that playing with knives is dangerous  To simulate this  you pretend to cut yourself with a knife and groan in pain  To emulate this  you actually cut yourself

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In computer science both a simulation and emulation produce the same outputs  from the same inputs  that the original system does  However  an emulation also uses the same processes to achieve it and is made out of the same materials  A simulation uses different processes from the original system   Also worth noting is the term replication  which is the intermediate of the two - using the same processes but being made out of a different material   So if I want to run my old Super Mario Bros game on my PC I use an SNES emulator  because it is using the same or similar computer code  processes  to run the game  and uses the same or similar materials  silicon chip   However  if I want to fly a Boeing 747 jet on my PC I use a flight simulator because it uses completely different processes from the original  there are no actual wings  lift or aerodynamics involved     Here are the exact definitions taken from a computer science glossary   A simulation is a model of a system that captures the functional connections between inputs and outputs of the system  but without necessarily being based on processes that are the same as  or similar to  those of the system itself   A replication is a model of a system that captures the functional connections between inputs and outputs of the system and is based on processes that are the same as  or similar to  those of the system itself   An emulation is a model of some system that captures the functional connections between inputs and outputs of the system  based on processes that are the same as  or similar to  those of that system  and that is built of the same materials as that system   Reference  The Open University  M366 Glossary 1 1  2007

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I don t think emulator and simulator can be compared  Both mimic something  but are not part of the same scope of reasonning  they are not used in the same context   In short  an emulator is designed to copy some features of the orginial and can even replace it in the real environment  A simulator is not desgined to copy the features of the original  but only to appear similar to the original to human beings  Without the features of the orginal  the simulator cannot replace it in the real environment   An emulator is a device that mimics something close enough so that it can be substituted to the real thing  E g you want a circuit to work like a ROM  read only memory  circuit  but also wants to adjust the content until it is what you want  You ll use a ROM emulator  a black box  likely to be CPU-based  with a physical and electrical interfaces compatible with the ROM you want to emulate  The emulator will be plugged into the device in place of the real ROM  The motherboard will not see any difference when working  but you will be able to change the emulated-ROM content easily  Said otherwise the emulator will act exactly as the actual thing in its motherboard context  maybe a little bit slower due to actual internal model  but there will be additional functions  like re-writing  visible only to the designer  out of the motherboard context  So emulator definition would be  something that mimic the original  has all of its functional features  can actually replace it to some extend in the real world  and may have additional features not visible in the normal context   A simulator is used in another thinking context  e g a plane simulator  a car simulator  etc  The simulation will take care only of some aspect of the actual thing  usually those related to how a human being will perceive and control it  The simulator will not perform the functions of the real stuff  and cannot be sustituted to it  The plane simulator will not fly or carry someone  it s not its purpose at all  The simulator is not intended to work  but to appear to the pilot somehow like the actual thing for purposes other than its normal ones  e g  to allow ground training  including in unusual situations like all-engine failure   So simulator definition would be  something that can appear to human  to some extend  like the original  but cannot replace it for actual use  In addition the pilot will know that the simulator is a simulator   I don t think we ll see any ROM simulator  because ROM are not interacting with human beings  nor we ll see any plane emulator  because planes cannot have a replacement performing the same functions in the real world    In my view the model inside an emulator or a simulator can be anything  and has not to be similar to the model of the original  A ROM emulator model will likely be software instead of hardware  MS Flight Simulator cannot be more software than it is   This comparison of both terms will contradict the currently selected answer  from Toybuilder  which puts the difference on the internal model  while my suggestion is that the difference is whether the fake can or cannot be used to perform the actual function in the actual world  to some accepted extend  indeed    Note that the plane simulator will have also to simulate the earth  the sun  the wind  etc  which are not part of the plane  so a plane simulator will have to mimic some aspects of the plane  as well as the environment of the plane because it is not used in this actual environment  but in a training room    This is a big difference with the emulator which emulates only the orginal  and its purpose is to be used in the environment of the original with no need to emulate it  Back to the plane context    what could be a plane emulator  Maybe a train that will connect two airports -- actually two plane steps -- carrying passengers  with stewardesses onboard  with car interior looking like an actual plane cabin  and with captain saying  ladies and gentlemen our altitude is currenlty 10 kms and the temperature at our destination is 24  C   Its benefit is difficult to see  hum     As a conclusion  the emulator is a real thing intended to work  the simulator is a fake intended to trick the user

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Simulator is something more broader than Emulator and it seems like the duality of this terms is overthought in the posts above   Emulator  People decided to use a new word emulation in the  computer world  when they started replacing some hardware parts of the existing system in straightforward manner - imitating their behaviour and relying on the computational nature to be sure to not break something and leave everything in the equivalent state  So we have emulated the piece of this   and the whole still works as before   Emulator usually used in narrow sense in digital area as replacement and virtualization - presenting in digital form as a piece of software - of something known and existed before  virtual chips  circuit boards  electronic devices   So when the world became more digital and brought the emulator word to the masses   the masses added uncertainty to it  or additional reasons    Simulator  First of all  I saw many comments about emulators do or replace something real but simulators not   BUT flight simulator is used for a real thing - it trains pilots  gives them skill up and knowledge and it replaces expensive real planes and saves much of money  And we cannot just say a plane-emulator because we have inner feeling that this is much more than that  so we call it simulator    Plane simulator could contain emulated radar or transponder that is true   Contra-statements that simulators are used for analysis and study  and emulators for something real   but that analysis and study not less a real thing than emulated GSM boards  even more in the informational age we live in   Analysis adds a value to the business  cuts costs or points out to profits not less than the replaced  emulated  hardware   Simulator is similar to modelling of something that we can t obtain for some reason  cost  technology  physical impossibility   It is usually simulated for something new or intangible or complex or not properly known to us like market  weather  combustion  user  So here comes the flight  black hole  stock exchange  simulations   So finally      Simulator is broader than Emulator    Simulator tends to imitate model more global processes things in general with ability to narrow the imitation down  e g  capacitor simulator with presets representing some known models      Emulator tends to imitate certain hardware devices with certain specification  known characteristics and properties  e g  SNES emulator  Intel 8087 or Roland TB-303    As for words origin  All came from Latin and mean      emulate is  to be equal   looks like more aggressive and straightforward - rivalry    simulate is  to be similar   looks like more sly and tricky - imitation

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Simulator  it is similar to interpreter  i e  it actually executes the real code in line by line to mimic the behaviour  Emulator  it is similar executable  i e  it takes compiled code and executes it

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The definitions of the words describe the difference the best  A google search gives the following definitions of simulate and emulate   simulate imitate the appearance or character of   emulate match or surpass  a person or achievement   typically by imitation   A simulation imitates a system  An emulation simulates a system so well that it could replace it or may even surpass it   In computing  an emulation would be a drop in replacement for the system it is emulating  Often times it will even outperform the system it is imitating  For example  game console emulators usually make improvements such as greater hardware compatibility  better performance  and improved audio video quality   Simulations  on the other hand  are limited by them being models  They are a best attempt to mimic a system  but not replacements for it  There are hardware emulators because hardware can be imitated and it would be hard to tell the difference  There is no Farming Emulator because there is no emulation that could replace actual farming  We can only simulate a model of farming to gain insight on how to farm better

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An emulator is a model of a system which will accept any valid input that that the emulated system would accept  and produce the same output or result  So your software is an emulator  only if it reproduces the behavior of the emulated system precisely

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Emulator   Consider a situation that you know only English and you are in China  In order to interact with a Chinese person you need a translator  Now  role of translator is that it will seek input from you in English and convert to Chinese and and give that input to the Chinese person and gets response from the Chinese person and convert to English and give the output to you in English  Now that translator and Chinese person is the emulator  Both combine will provide similar functionality as if you were communicating with the English person  So hardware may be different but functionality will be same   Simulator   I can t give better example than SPICE or flight simulator  Both will replace hardware component behavior with the software or mathematical model which will behave similar to the hardware   In the end it depends on the context that which solution better suits project needs

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Simple Explanation   If you want to convert your PC  running Windows  into Mac  you can do either of these       1  You can simply install a Mac theme on your Windows  So  your PC feels more like Mac  but you can t actually run any Mac programs   SIMULATION     or       2  You can program your PC to run like Mac  I m not sure if this is possible  P    Now you can even run Mac programs successfully and expect the same output as on Mac   EMULATION    In the first case  you can experience Mac  but you can t expect the same output as on Mac   In the second case  you can expect the same output as on Mac  but still the fact remains that it is only a PC

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Some years ago I came up with a very short adage that  I believe  captures the essence of the difference quite nicely      A simulator is an emulator on a mission    By that I mean that you use an emulator when you can t use the real thing  and you use a simulator when you can t use the real thing and you want to find something out about it

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The distintion between the two terms is a bit fuzzy   Coming from a world where  Emulators  are pieces of hardware that allow you debug embedded systems   And remember products that allowed you to have ICE  In Circuit Emulation  capabilities to debug a PC platform  I find the use of the term  Emulation  to be a somewhat of a misnomer for software that SIMULATES the behaviour of a piece of hardware   My justification for the current use of the term is Emulation is that it may  augment  the functionality  and only is concerned with a  reasonable  approximation of the behaviour of the system     ICE   In Circuit Emulation  A piece of hardware that is plugged into a board in place of the actual processor   It allows you to run the system as if the actual processor was present   Typically these have a variant of the processor on them to actually execute the software with glue logic to allow the user to break executation and single step under hardware control   Some would also provide logging capability   Most modern processors development systems have replace ICE type emulation with JTAG Emulation  where the JTAG just talks to the processor via a special purpose serial link and all execution is perform by the processor mounted on the board   Software EMULATOR  An 0x86 emulator is only concerned with being able to execute 0x86 assembly language  not providing accurate cycle per cycle behaviourial model of a SPECIFIC 0x86 processor   Bochs is an example of this   QEMU does this  but also allows  virtualization  using special kernel modules   SIMULATOR  Texas Instruments provides a CYCLE ACCURATE behaviourial model of there processors for software development that is intended to be a accurate SIMULATION of SPECIFIC processor cores behavior for the developers to use prior to having working hardware   Software EMULATOR augmenting functionality  BLEEM not only allowed you to run Playstation Software  but also allowed the display to be output with higher resolution than the Playstation was able to provide  and also took advantage of more advanced capabilities of GPUs that were avaliable    i e  Better blending and smoothing of textures

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A simulation is a system that behaves similar to something else  but is implemented in an entirely different way  It provides the basic behavior of a system but may not necessarily abide by all of the rules of the system being simulated  It is there to give you an idea about how something works   An emulation is a system that behaves exactly like something else  and abides by all of the rules of the system being emulated  It is effectively a complete replication of another system  right down to being binary compatible with the emulated system s inputs and outputs  but operating in a different environment to the environment of the original emulated system  The rules are fixed  and cannot be changed or the system fails

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Both are models of an object that you have some means of controlling inputs to and observing outputs from   The key difference is that    With an emulator  you want the output exactly match what the object you are emulating would produce  With a simulator  you want certain properties of your output to be similar to what the object would produce    Let me give an example -- suppose you want to do some system testing to see how adding a new sensor  like a thermometer  to a system would affect the system  You know that the thermometer sends a message 8 time a second containing its measurement   Simulation -- if you do not have the thermometer yet  but you want to test that this message rate will not overload you system  you can simulate the sensor by attaching a unit that sends a random number 8 times a second  You can run any test that does not rely on the actual value the sensor sends   Emulation -- suppose you have a very expensive thermometer that measures to 0 001 C  and you want to see if you can get by with a cheaper thermometer that only measures to the nearest 0 5 C  You can emulate the cheaper thermometer using an expensive thermometer and then rounding the reading to the nearest 0 5 C and running tests that rely on the temperature values   Note that simulations can also be used for forecasting or predicting behavior  Finite element analysis simulations are used in many applications  including weather prediction and virtual wind tunnels   The definitions of the terms    emulation -- surpass or exactly match simulate -- imitate in appearance or character

[terminology] Simulator or Emulator? What is the difference?

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