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;In the world of computing, terms like "[[Hypervisors|hypervisors]]", "[[Simulators|simulators]]", "[[Compatibility_layer|compatibility layers]]", "[[Wrappers|wrappers]]", "[[FPGA|FPGA-based hardware cloning]]" and "[[:Category:Emulators|software emulators]]" are often used interchangeably, leading to confusion. While they share some similarities, each technology serves a distinct purpose and operates at different levels.
Within the realm of computer science, emulation occupies a niche distinct from virtualization or other techniques. Whereas hypervisors usually used for partitioning physical hardware resources among multiple guest operating systems, and simulators where developers build virtual replicas of specific environments or processes, emulation endeavors to recreate an entire historical architecture. This digital reconstruction seeks to faithfully capture the instruction set, timing behaviors, hardware features and even peripheral nuances of a bygone hardware platform. Unlike compatibility layers, which translate software instructions to a native format, emulation builds a virtual stage upon which the software itself can perform authentically. Emulation's intricate tapestry sometimes intertwines with threads of other technologies though. Notably, certain emulators leverage hypervisors for a more efficient handling of resource allocation and isolation. Additionally, some emulators employ compatibility layers as subcomponents, acting as translators for specific libraries or APIs that might otherwise be incompatible with the host environment. Think of these layers as linguistic bridges, allowing the emulated software to converse fluently with the modern system hardware. By strategically merging these techniques and the help of skilled use of [[High/Low_level_emulation|HLE and LLEor Hybrid]], [[Dynamic_recompilation|compiler techniques]] and using specific features such as Fast Memory Access[https://github.com/PCSX2/pcsx2/pull/5821][https://github.com/PCSX2/pcsx2/pull/7295][https://yuzu-emu.org/entry/yuzu-fastmem/#what-is-fastmem][https://dolphin-emu.org/blog/2016/09/06/booting-the-final-gc-game/] and instruction set support (such as [https://whatcookie.github.io/posts/why-is-avx-512-useful-for-rpcs3/ AVX-512 for RPCS3]) and other various optimizations[https://yuzu-emu.org/entry/yuzu-progress-report-dec-2023/#android-adventures-and-kernels-with-benefits], certain emulators achieve impressive levels of performance and compatibility, further unlocking the doors to historical software [[Preservation_projects|preservation]].[https://youtu.be/cCXri4yDHmU]
So in summary, an accurate emulator is when an instruction given to both the program and the hardware results in both outputting the same result. That means accurate emulators produce much fewer audio and video glitches, usually at the cost of more processing power needed. It's often achieved by using tighter synchronization. The more accurate an emulator is, the lesser deviations there is from real hardware behavior but the more demanding it is. Ironically, that aspect might at times be at odds with how authentic the experience is, when it introduces [[Input lag]]. A similar debate surrounds CRT shaders as well. Not to mention the hardware intensive nature of very accurate emulators for later consoles may be at odds with the emulator's usability, especially with the recent collapse of Moore's Law (in layman's terms, you can't just "buy a better PC" if semiconductor technology does not catch up fast enough with what it takes for accurate emulation that makes zero compromises for optimizing speed). As a result, accuracy and emulator authenticity continue to be controversial subjects and highly a matter of opinion depending on what aspect of the experience the user values more.
===High accuracy===
High accuracy is a level of precision that emulator developers strive for when achieving [[#Cycle_accuracy|cycle accuracy]] or even [[#Partial cycle-accuracy|partial-cycle accuracy]] is not practical or necessary. This approach focuses on replicating the original system's components as accurately closely as possible, aiming to faithfully reproduce its behavior while staying mindful of hardware demands. Though it may demand more processing power compared to low lowly accurate emulators, pursuing a more accurate emulation experience can pay off in the form of fewer audio/visual glitches and better handling of niche scenarios that creative programmers often implement. Though they don't mimic every clock cycle as precisely as cycle-accuracy, highly accurate emulators capture the essence of the original hardware very well. Also achieving 100% compatibility with commercially released games is a common goal for emulators with high accuracy. Some of these emulators represent an even more meticulous level of precision in replicating the original system compared to other highly accurate emulators, this heightened level of accuracy often involves more sophisticated techniques, demanding increased computational resources.
===Cycle accuracy===
====Partial cycle-accuracy====
This focuses on replicating the timing of instructions and key internal operations, while simplifying or skipping some less critical details. This can lower the performance requirements compared to full cycle accuracy. Remember, just because an emulator is partially cycle-accurate doesn't necessarily make it more accurate than a highly accurate emulator. For example, CEN64 only emulates the CPU pipeline cycle-accurately and that's all, on the other hand Simple64 is more accurate in terms of timing for specific tasks like certain DMA transfers, even though it doesn't achieve partial partially cycle-accurate emulation.
:Examples of partially cycle-accurate emulators are [https://old.reddit.com/r/emulation/comments/vy8cg7/ares_v129_has_been_released_crossplatform/ig4da06/ bsnes] and [https://discord.com/channels/976404869386747954/976463759935696977/1106700321222299762 CEN64].
====Cycle-based accuracy====
This type of emulation accuracy aims to reproduce the system's functional behavior within a specified number of cycles without necessarily adhering to the exact
timing of each individual instructioncycle. Since this method doesn't go out of its way to mimic the precise timing and execution of each instructioncycle, it may not be able to handle all hardware edge cases.
:An example of a cycle-based emulator is jgnes with its cycle-based emulation of the Ricoh 2A03 and PPU.
