20GB and 60GB Models
Early models of the PlayStation 3 that featured 20GB and 60GB hard drives are fully compatible with all PlayStation 2 software. These versions of the PlayStation 3 console featured many internal components that were also present in the PlayStation 2. The Emotion Engine processor is physically hardwired into the motherboard architecture, perfectly emulating the functionality of the original PlayStation 2. There are no upgrades or additional steps required to play PlayStation 2 games on these versions of the PlayStation 3.
80GB Model
The first PlayStation 3 consoles with 80GB hard drives were released with software-based PlayStation 2 compatibility in mind. Rather than relying on physical Emotion Engine architecture, this model utilized software emulation to play PlayStation 2 games. The Sony PlayStation Store offers a free, downloadable PlayStation 2 emulation package that replicates the Emotion Engine functionality. This Emotion Engine emulation software, however, is not compatible with all PlayStation 2 games, and a firmware update is required before the software can be installed.
Incompatible Hardware
The later versions of the 60GB and 80GB PlayStation 3 consoles were released without any backwards-compatibility options for PlayStation 2 software. The 40GB model also lacks a method to play PlayStation 2 discs. The PlayStation 3 Slim, a streamlined version of the console, lacks many features that are present in previous models, including PlayStation 2 compatibility. Sony has no plans to release a new version of the PlayStation 3 that contains either a physical or software-based Emotion Engine.
PlayStation 2 Game Downloads
Sony introduced downloadable PlayStation 2 software to the PlayStation Store in October 2011. These games work on any hardware revision of the PlayStation 3 by packaging Emotion Engine emulation with the game itself. Each game is specifically optimized to work with a unique version of the Emotion Engine. Unfortunately, the amount of available games is very small in comparison to the actual size of the PlayStation 2 game library. A majority of PlayStation 2 games will never be made available in the PlayStation Store.