A x86 CPU with the following features is emulated:
Pentium class CPU
x87 with bit exact 80 bit floating point numbers
PAE support
CMOV instructions
MMX and SSE2 support
AMD Virtual Machine extensions (SVM) with Nested Page Table support
RDPMC support to read the instruction count
Known limitations:
No segment limit and right checks when accessing memory
No debug support (DRx registers)
从这个网页提供的技术信息来看，对 x86 的仿真，在技术上是很复杂、很困难的。这么困难，都能搞成，原因是 x86 的普及度高，软件丰富。否则，如果没有丰富的软件，仿真的动力就会消失。假如将来普及了某个 risc 的 CPU，那时候，仿真的难度就会降低。