Hi Nadeem,Thank you for using the Xerox forum.
The main differences are speed and toner type.
I would suggest that you review the Xerox Support & Drivers site for complete answers to your question.You can enter the model in the center search box and then select support.
On the right column is a product specifications link (shown below)
The 2 models support pages are linked here D125 and 120EA
You also may consider using our "Contact an experienced service technician" program at the following link Fast Track to the Expert
Please share some one, architectural difference between xerox d125 and Nuvera 120EA models.