PS3 Game emulator is an application which can be used to run PS3 games on your PC. What you do is, install that emulator and put the DVD in and play the game. But how its going to work?
PS3 too is a system with same components as PC except that it is designed for gaming. So, you can just run a similar application on you Windows or Mac and play the games on them. There is a windows version and I am not sure whether there is any Mac version of the emulator. Very similar to the PS3 emulator, there are emulators for Xbox too. That application will allow its users to play the xbox games on the PC or Mac. Same here, no idea about the availability mod for Mac.
In a very similar manner, you can have linux os in your PS3 to know more visit here.
Why to run Linux OS on your PS3? - I really cant tell you any reason with my knowledge.
Will it be faster or Slower? - This depends on the version of PS3 and the PC, there can be cases where both may be on the top. That means, your PS3 can be faster or your Xbox can be faster. If you want to know the affect of the emulator running on the PC, it is defintely affective. But it will depend on how it is accessing the hardware to run the game. If it takes control in a deeper level, that has very low and positive affect sometimes, and if it takes control of the hardware in much higher level, it shows some slowing affect.
Know how you can make backups of your games. More here.
Why to use these emulators? - If you have bought the PS3 disc already and does not want to buy a new disc for your PC to play on PC. And if you think, you facing some problem with your PS3 either in game or outside the game, these emulators are needed for you.
What are the disadvantages? - You may find it difficult to shift between PC and Xbox and to get used to them in the game controllers. Some of the Xbox Controllers work for PC too as far as I know.
Is it wise to use different consoles and controllers? - Some gamers think it is a nice experience to deal with PS3, Xbox. They like to experience a new thing little. But if you ask me, let me tell you, there is no way it will get to an end if you are trying to try new things. That too in a faster world like this. It will just go the way of using cell phones. If you want to change your phone every time Nokia releases one, you may have enough to spend but you end up confused what to do in a new phone always. Your knowledge will be improved, but your efficiency might decrease. I can say, sticking to a thing is nice, upgrade in same field if you want to. In competitive examinations too, our seniors used to suggest us to use a single book to gain knowledge. You might think that you will get more knowledge if you are referring to 2 to 3 books. But books are unlimited, your time is limited, you just end up confused what the actual concept is.
