This thing is called a 5D optical data storage crystal. It's a little piece of fused quartz, etched to remarkable precision using a femtosecond ultraviolet laser.
The "5D" part of the name is just a marketing gimmick (it only has three dimensions, obviously), but it's impressive anyway. Using current technology, these little things can store 360 terabytes of data. Once written, these crystals can survive temperatures up to 1000°C, and could theoretically last for billions of years.
@Chickiepup I'm pretty sure you'll be able to load one of these discs before the Sun dies. Which is an improvement over DAT tapes.
Sunbeam City is a anticapitalist, antifascist solarpunk instance that is run collectively.