An answer from Werner Vogels, CTO of Amazon, on the story that Amazon Web Services was created to use Amazon.com’s spare capacity during quiet periods.
The excess capacity story is a myth. It was never a matter of selling excess capacity, actually within 2 months after launch AWS would have already burned through the excess Amazon.com capacity. Amazon Web Services was always considered a business by itself, with the expectation that it could even grow as big as the Amazon.com retail operation.
I’m finding some of the answers at Quora to be interesting, and am surprised at who is active on there.