The 1,000,000 number comes from leozzyzheng's post on the first page, I was pointing out that if you can handle ticking for 1000 players on independent chunks you can handle 1,000,000 at 1000 sharing each chunk.
Although I'm not sure about the 20 GiB number as a max. With NUMA and multiple memory controllers you can load in more in parallel. Looking at the specs of something like the dell R920 (dells top of the range server) should theoretically be able to go up to 8 parallel DDR channels, so you might with a befy enough server be able to go up to 160 GiB/s. But thats only 8 times as much data, and I have no idea about how much the server would be able to take advantage of that sort of memory architecture.
Although I'm not sure about the 20 GiB number as a max. With NUMA and multiple memory controllers you can load in more in parallel. Looking at the specs of something like the dell R920 (dells top of the range server) should theoretically be able to go up to 8 parallel DDR channels, so you might with a befy enough server be able to go up to 160 GiB/s. But thats only 8 times as much data, and I have no idea about how much the server would be able to take advantage of that sort of memory architecture.