When your computer calculates that (or anything), it uses the RAM. If for example, you have 2 gigabytes of RAM (which is typical), it can, at most, use 2GB = 2048MB = 2097152KB = 2147483648 Bytes = 17179869184 binary places (like decimal places, but in base 2). Actually, half that amount, because one of the binary digits will be a positive or negative sign. I don't know exactly how much bits does the floating point take, so it might be even less bits. There is simply no more room in the RAM to work with, unless you save it all to the hard disk, clear the RAM and go from there - that's what the article means by "make your own storage".

I hope I was clear. I hope that I was right (though I expect to be unless there is an even stricter limit somewhere that I don't know about).