VG247

Halo Anniversary will allow players to switch back and forth between classic and updated graphics in real time, because the game is essentially running two engines simultaneously.

Executive producer Dan Ayoub IndustryGamers that Anniversary will feature a “classic mode”, accessible via a controller button.

To achieve this, 343 have the game’s original engine powering the gameplay, with a second one, created in collaboration with Saber Interactive, running on top to make everything beautiful.

Making this work is said to have been a “tricky process”. You think?

In not building a completely new engine, 343 is sticking to Frank O’Connor’s vow that the new Halo developer will “never try to replicate what Bungie did”, and will “never ignore the roots and foundation of what makes Halo successful.

http://www.vg247.com/2011/06/10/halo-anniversary-to-run-two-engines-side-by-side/

Not the first game to do that but it is pretty cool.

Sounds good however it does not mean much until I am playing it.

That's a pretty cool little feature.