HDD Platters
These platters are taken from hard drives that has been dismantled.
The big one on the left is from a very old open air hard drive, it had 6 platters like this one and the case was of plastic and completely open, ca. 70's tech.
The 3 platters in the middle are from 5.25" hard drives ca. 80-90's tech.
The last 3 are from 3.5" hard drives ca. 90's tech.