In short: it plays far too well (~2500 ELO.) People think it originally played at a reasonable level and accidentally got more powerful as the seatback computers got more powerful; the same thing happened to the Mac chess app with the release of the M1.
That would be exceptionally sloppy development. Phones have had more than enough power for long enough. 4 core Skylake (Mac 2016) would be well beyond human capabilities, if it's just raw power.
The "thinking" (difficult) limit should be considered moves ahead, both depth and count. With a possible limit to time, if there is any time control.
> 4 core Skylake (Mac 2016) would be well beyond human capabilities
Not if the computer's time limit is set at 15 microseconds. It's not a question of whether the computers have "enough power"; just whether they are more powerful now than they were previously.
And yes, obviously that's a very sloppy and error-prone way to implement a difficulty control.
Even a computer from 20+ years ago will comfortably crush Carlsen, it really goes down to the specific engine used, chess engines have evolved a lot during the years.
Carlsen knows how to play anti-bot chess where some engines may struggle, but that only applies to amateurish engines.
> the same thing happened to the Mac chess app with the release of the M1
I fired up Chess shortly after getting an M1 and got destroyed a bunch of times. I thought that I was just extremely out of practice and quit playing for years. I guess it's better to find out late rather than never.
Precisely a Core Duo and a custom build with -O3 -ffast-math (a Chess engine doesn't requiere anything further from integers) and -march=$YOUR_CPU_THERE can yield crazy performance speeds without needing an m4 and a great match even for masters.
