PlayStation 2's use the emotion engine as a processor, which was removed from PS3s to save money.
This killed off PS2 backwards compatibility, but Sony has a new software solution.
A patent filed by Sony has a method for the cell processor to emulate the emotion engine which can bring PS2 backwards compatibility to all PS3s.
To quote: There are two main ways to emulate hardware. Interpretation is when target code is decoded and converted into a language the host can understand. The other strategy is to decode and recompile programs in the host's language.
Maybe the concept is better explained another way. Interpretation is like having someone constantly translating English to Japanese for you, non stop, twenty four hours a day wherever you go. Decoding and recompiling is like someone translating a sets of words and putting them in a dictionary you can reference.
Sony developed a way to translate instructions from an Emotion Engine chip into chunks that can be referenced.
Figure 2 from the patent is a schematic drawing of how the system works. Figure 3A is a drawing of the PlayStation 2's chipset. Figure 3B is the emotion engine. Figure 4 is where the whole story gets interesting! It's "an example of a host system based on a cell processor that may be configured to emulate the target system." The target is figure 3B, the Emotion Engine.
There aren't too many reasons why Sony would want the PS3's Cell processor to emulate the PS2's Emotion Engine and the key one is backwards compatibility.
Perhaps, a firmware update or the new PlayStation 3 slim, which Ars Technica say is coming this fall, will utilize this technology.
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