The NEC ND4650A DVD burner was first spotted in May 2006 but seems to have been developed earlier already. Unlike most other drives, the 4650 and 4651 are attached via an S-ATA interface. The NEC ND4651 burner adds support for LabelFlash but both drives - together with the ND3650 and ND3651 - share the same hardware and only differ in firmware. However you should not try to simply flash a NEC 4651 firmware on a NEC 4650 drive or vice versa. This will NOT work.
Click here for detailed specifications of the NEC ND4650A and ND4651A.
The following firmwares are available for download here:
Overview on the used writing strategies