Ps2 game emulation is still difficult for a pc to handle. There are tons of websites that go into great detail explaining the challenge of the pc having to essentially translate one language set to another. The ps2 hardware was also vastly different from pc architecture. These posts explain it a bit.
“when your modern computer is running a PS2 emulator and you're playing Grand Theft Auto and drive your car off a ramp, the computer doesn't simply calculate the trajectory for your car - it does a calculation of "what would a playstation2 calculate for the trajectory of a car." This extra step occurs for EVERY calculation the game makes and significantly slows things down.”
“Despite a large interest in PS2 emulation due to its sizable collection of games, it is still one of the hardest consoles to emulate for a number of reasons. First of all: many people believe that since the main CPU (Emotion Engine) runs at a clock speed of 294Mhz (299Mhz on later revisions), it would make emulation easy on recent hardware. But this is not the case, because the clock speed of the emulated CPU is not necessarily indicative of the ease of emulation. Specifically, the PS2 CPU contains a multitude of custom sub-components and chips such as the FPU co-processor, 2 Vector Units, IOP, SPU2, Graphics Synthesizer and SIF which together work asynchronously to comprise the 128-bit Emotion Engine. In order to emulate them perfectly with correct timing requires an enormous amount of power. Moreover, the PS2 just like PS1 uses the MIPS architecture instead of standard x86 code, thus making emulation slower.
Another big problem is the emulation of PS2’s own floating point unit (FPU) because it doesn’t follow the IEEE standard. To keep it simple, just changing a couple of numbers will cause glitches to occur to the game’s graphic (VU) and logic (EE), resulting in things like broken AI, odd behaviors or graphical bugs. While PCSX2 allows for the option of either clamping/rounding on both VU and EE as a solution to fix these glitches, it remains by far not the most accurate way to emulate the PS2 FPU.
To conclude on the problems with PS2 emulation, we come to hardware rendering. The PS2’s graphics pipeline acts very differently from modern GPU cards and emulating it in HW mode with any degree of accuracy is difficult. This is due in part to the versatility of PS2, fact that it doesn’t use fixed shaders, or that even the games themselves do not use a consistent formula to achieve different graphical effects. Various type of emulation enhancements like display resolution scaling leads to the typical “black lines glitch” because of the use of a non-integer resolution. While the OpenGL backend on PCSX2 greatly improved on many of these issues, most games still require “software rendering” to fix many common glitches, which in turn slows down the emulation. Although Games using mip-mapping (Ratchet & Clank, Ace Combat, etc...) and games running on the Snowblind Engine are playable in OGL HW mode with minimal problems on high-end PCs.
In summary, it is not possible to achieve close-to-perfection PS2 emulation with actual PC hardware, and even if it was possible, the results would most likely be unplayable. The PS2 is simply a very complex machine that even game developers struggled to work with. "
