How to make out the diffrences b/w one release to another release in ABAP?

Hi,

We have an upgrade project which needs upgradation from 3.1i to ECC 6.0. I would like to the diffrences between 3.1I to ECC 6.0. Can any one help me in finding out the same OR any URL where i can get the whole information on this. I would appreciate ur immediate response.

Thanks in advance to all SAP gurus.

Regards,

Raju.