What is it?

This was a poster put up in 1978 explaining something. Who put it up and what is being explained?
If it’s there and you can see it—it’s real
If it’s not there and you can see it—it’s virtual
If it’s there and you can’t see it—it’s transparent
If it’s not there and you can’t see it-you erased it!

What is being talked about?

PS: Googling will give you the answer but not the satisfaction!!

Nikhil Bhaiya,ayesha and interstellaroverdrive hits the BINGO.Its the IBM poster talking about the properties of RAM.