How does GPU-Z "decode" nvidia vbios ? (also pascal bios modding)

[TheQuentincc]

Hi, I would like to understand how nvidia pascal vbios work, I already found a thread talking about TDP, temp, clock value in the vbios (with an hex editor) and also an other thread which present a software (mobile pascal bios tweaker) that can also "modify" the vbios checksum but I didn't found how GPU-Z creators figured out the memory support of the card in the "advanced > NVIDIA BIOS" section or where they found it.
Can someone tell me how to find these value and/or where are they located in the vbios ?
(also if you have any link to share about vbios modding or understanding it, feel free to share it )
Thanks you all