bios chip

I have a WD 1600AAJS HDD with 2060-701444-003 RevA controller board.

https://www.hddzone.com/wd1600aajs-wd-pcb-2060701444003-rev-a-p-1145.html

I purchased one of your boards but can you tell me which is the bios chip I must swop out?

The PCB’s BIOS is integrated into the Main Controller IC. You should exchange the Main Controller IC to let the HDD be recognized. Move the Main Controller IC(the biggest chip on the board) is a complex job which need you have certain technique. Some electronics repair shop can do it.

But which do you consider to be the biggest chip?? The Marvell (square) or hynix (rectangular)?

The square one.