You could fit the data from 25 million 1TB SSDs on this 5cm diamond wafer

pcgamer.com:

Researchers in Japan say they've concocted a new method of creating wafers out of diamonds able to store mammoth amounts of data on them. We're talking 25 exabytes of storage, which is a 25,000 petabytes. Or 25,000,000 terabytes. Or 25 billion gigabytes. It's a dizzying amount of data, that's for sure.

If you assume there's roughly 50,000 games on Steam and each one is around 80GB, which to be completely honest is probably a gross exaggeration of the average game install size on the platform, you'd be looking at around four petabytes of data required to install the lot. So with a single diamond wafer you could save the entire Steam catalogue 6,250 times. 

Though there's likely room for much more if you factor in how many visual novels there are on Steam.

Now it's not like this diamond wafer will act like a disc you throw into your machine. This is quantum storage, and it uses a defect in diamond, known as the nitrogen-vacancy center, to store a quantum bit, or qubit (via New Atlas).

This defect in diamonds has proven quite useful already in use for quantum computers, as it allows researchers to read out the specific spin of an electron. That's a key part of how a quantum computer works, along with quantum entanglement, and how they might one day reach a point of utility for computing workloads far beyond what is possible with a classical computer today. These diamond qubits are even useful at room temperature, which means less reliance on super-cooling gases that many quantum qubits require to operate.

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