Question about HDD technology used in my drive


I’ve just purchased HDD at amazon which was labeled as WD NAS PLUS. It is WD80EFAX. My old, 3TB drive is WD30EFRX. So my first question is related to visual differences. First one has flat surface and steep shaped corners, this one is different, both were purchased as NAS PLUS drives. I have seen images where some 8TB nas drives are look like my first drive. So what’s difference?

Secondly, I just can’t find any information whether my drives use helium instead of air. How to get full specifications based on serial number and so on?

Thanks a lot!