when you bought and installed it it should have said what you bought, and on the chip itself. open it up and read the label if nothing else.
Also you can just turn on your xbox, and go to your BIOS screen, and it will tell you there, what kind of Chip you have (if you don't want to open up your system). To get to the BIOS screen, you can hold R L START SELECT and it should take you back to the BIOS screen. If not that way, Just press both the EJECT and POWER button on the Xbox, to get to the screen (the light indicator around the eject button will be a pinkish color).
