Here you find the HP update SP26522.
HP dvd640 revision b Firmware Update
This is a firmware update for the HLDS GWA-4084B 8X DVD(+/-)R/RW DL LS
Inside the firmware there are the strings: 'DVDRRW GWA-4161' and 'HP DVD Writer 540b A19305/03/15'. The strings 640 and 4084 do not occur at all.
Inside the flasher you find 'HP DVD Writer 540b', 'HP DVD Writer 640b' and 'HL-DT-ST 4161B EME'