retrolefty:
It's a hard disk data platter from a very old school disk drive, circa minicomputer and mainframe era. Read/write heads would be positioned over the proper track and the data would be read or written to it. Ones I worked on had ten such disk platters stacked on a single spindle. Spare platter cartridge would cost around $1K so making backups was not a cheap operation.Lefty
Wow, that was good background on this type of things. The donor did mention it came out of an ancient large hard disk drive. Nowadays we don't distinguish among hard disk, hard drive or hard disk drive and I just realized how ridiculous it is (with silly me included for the last 20 years). The hard disk is this platter pictured above, and the drive is like a washing machine!!! (hint, I don't want the washing machine) It's like calling the desktop computer case the CPU, while the real CPU is the processor that sits inside of the case. I'm sure if I lived to 250 years old I would hear this type of mistakes a lot. 