How to sort millions of rows of data in a file with less/meagre memory

Question

(From here)

I attended an interview last week and this question was asked:

How do you sort a billion rows of data in a file with only 640KB of memory in

Answer 1

I'd use the GPU! Even on a fast computer, the GPU is often faster at sorting. And I don't know how big the "rows" are, but it's not hard to find 1GB video cards, so that answers the storage question, too.

Besides, if I had to work on an 8080, I'd definitely want to put the sweetest graphics card I could find on there.

You just have to be ready for the follow-up question: "How do you get an 8080 to talk to a modern PCI Express 2.0 x16 card?". I have discovered a truly marvelous method, but this textarea is too narrow to contain it.