Its speed was thanks to the sheer amount of effort that was put into hand crafting assembly code. The assembly code was heavily optimized for the Pentium processors of the day. While it locked the emulator to a single operating system, it did prove to be a significant enough speed improvement.
Atari PC Emulator boosted server other features such as full collision checking, the support for every single bank switching scheme. The ability to emulate the Atari’s vast amount of controls, among a vast amount of other features helped set Atari PC Emulator apart from all the others early on. Sadly though, development of the emulator ceased in 2002.