Most games don't care what your system is. DOSBox works well for anything not so fussy and meets most cases of 'i just want to play this damn dos game on my damn pc'.

You might like PCem for the other. Having the game's speed limited by MHz, cache, and video bus is a lot more consistent than a cycle amount....

If the goal of emulation is seen as preserving the function of certain hardware any deviation from the original has to be seen as "faulty emulation" as you call it. Therefore, this article is a pretty good example why you shouldn't even dare about talking accuracy with 5th gen and later console emulators. Even if someone were to write an emulator targeting near 100% accuracy the hardware for this isn't there yet considering that accurate SNES emulation already requires a quad core CPU. I still consider it a technical feat that PCSX2/Dolphin are playable on modern hardware, but those emulators are so quirky that it's more of a mere approximation than an emulation to me.

Now if you are talking about the average emulator user who prefers his pirated game with stretched 1920x1080 output with some anti-aliasing and unfitting shaders plastered all over it the whole accuracy business is just moot anyway...

To be completely honest, if whatever emulator I'm using looks and acts enough like the real system it's emulating, then it usually meets my standards. Whenever possible I'll usually seek out the most accurate emulators available for any given system, though admittedly sometimes it's easier to go with a slightly-less accurate emulator if it offers a better user interface or emulation of certain peripherals. As well, given the limitations of current-day PC hardware, it's almost completely pointless to try and find an accuracy-focused emulator for any system more advanced than the PSX.

Compared to emulators for well defined systems like a C64 (Vice, CCS64 etc.) Dosbox is not accurate.
But the PC platform itself is open in terms of components you could exchange. So e.g. a cycle exact emulation is just nice to have, but not required. For a C64 platform most software simply don't work on a non cycle exact emulation.

It is much more important to have a good approximation of the common similarities, like what Soundblaster compatible means from software side.
Or for GUS emulation it doesn't implement the drop down in sampling rate up to 19 kHz for 32 voices but that is originally happening on the hardware back end of the card and not seen by software.

Accuracy is required at every interface that directly interacts with software, including correct implementation of machine code emulation. From my experiences with dosbox, there seem to be still some flaws for FPU handling in PM.

If you ask, what is enough it strongly depends on your personal preference. Some like to have profiles for different analog monitor types and their distortions and sound for floppy head movements, virtual fans etc.

Thank you for the insightful replies. It echoes the stated goals of the various gaming emulators; particularly DOSBox: "..it can run plenty of the old classics". DOSBox is designed as an emulator for DOS games. Also, I interpret these posts as pointing out the technical limitations of highly accurate emulation and the difference between different hardware systems; that console emulation is not the same as for the PC, and that certain parts of emulators are more crucial than others (for example, the machine code in PC emulation, as stated above).

I think that a gaming emulator is good if it supports the major portion of (popular) games, or at least that expected by the "community". The "bit for bit" emulation should be relegated to separate projects or, in the case of the PC, Bochs, to preserve old hardware. However, in the case of DOSBox, it should preserve games first, and the accuracy in hardware (a distant) second. There is a balance here, but I would agree that the gaming emulation is correct if it runs games, and not incorrect if the hardware isn't 100% emulated. In the case of the SNES mentioned above, there may be a few percent of games (or more?) which are not playable without near perfect emulation, but I don't see the equivalent measure among the DOS games. I certainly don't view posts often about DOSBox failing half-way through a DOS game, but there are requests for near perfect accuracy among the "non-standard" modes (standard as defined by the emulator itself as a focus for development).

The holy grail of emulating a system is doing on a level of "cycle accurate". That is, you are able to simulate the system 100% like the real hardware, quirks included, and do it at the proper speeds. It is very difficult to do that in software and it only gets more complex as your port the emulator to different platforms and add various emulated peripherals. Game systems in particular are notoriously difficult to emulate because their timing is based on NTSC or PAL frequencies. Most computers don't have any way to generating a reference clock at those now oddball values.

PC emulators are an interesting batch since they all have different goals. Bochs is designed to be a 100% portable PC emulator written completely in C. DOSBox only attempts to simulate a DOS environment with common PC peripherals. PCEm is actually pretty rare in that it emulates a PC's chipset and runs a real BIOS and option ROMs. Most of the common VM software uses a BIOS written specifically for it (in native code) and only emulates the minimum possible for performance reasons.