Why does emulation require X amount of cpu to for accuracy?

Question

This is something I am having trouble wrapping my head around. Say for example PCEm. It can emulate up to Pentium II, however Pentium III is nearly impossible due to current hardware restraints. However, a Pentium III is 433mhz (if I remember correctly) and modern CPUs are well into 5ghz range. However, to accurately emulate a 433mhz you need x amount of CPU.

Why is that the case? If the CPU you’re using to perform the emulation is vastly more powerful?

I read it’s same even for the Super Nintendo, it ran 5mhz, and for accurate emulation you’d need 3Ghz (which is around today, but wind back a few years ago it would the the same question).

Hopefully it makes sense, I am still trying to understand emulation on a deeper level. Happy to have any links to any docs that answer this question as well.

In: Technology

Answer 1

Before you understand emulation you need to understand translation. Which is quite simple.

Take for example arm and x86 on old and new mac. Their cpu dosnt speak the same language. So the cpu will have to translate the old x86 instruction to the new arm instruction.

So imagine the CPU as an English guy who is given a Japanese book and is translating it word for word and doing what the book says.

He sees the phrase “手を挙げて”, translates it to “raise your hand” and then he raises his hand.

So far so good.

Next he sees “ヒナから手紙を受け取って”, translate it to “recive letter from Hina”, then… wait who is Hina? What does the letter say?

Translation no longer works.

So instead of just translating the instruction he needs to pretend to be Hina and write that letter (in japanese), then seal it, then deliver it to himself.. This is emulation.

Emulation is much more work because he (the cpu) is doing the work of multiple people (the device) all by himself in a language he dosnt understand. Just to make that instruction make sense.

So if you want the emulation to work in real time like for a game, the cpu needs to be much more powerful than the cpu of the emulated device. Since that cpu isn’t just translating and performing the instruction, but also the interaction between all the other devices connected to it.