component of microcontroller

what is that rhombus shaped ic called.what is the function of the ic

Moderator edit: ridiculously large image replaced with something reasonably sized

Your image is way to big.

The mega8u2? It acts as a virtual com port. Lets you talk to the arduino / upload code with a standard usb connection.

How many topics about the same thing do you plan on starting?

There is no rhombus shaped chip. It is simply a square chip rotated through 45 degrees.