Amazon recently launched their latest Web Services Product, which aims to help you store data for the long term. Amazon Glacier costs one cent per gigabyte per month to store data, with some limitations on the retrieval. It costs $0.12/GB to retrieve data if you need to access more than five percent of what you stored. It also will take a few hours to retrieve the data.
Given the very low price and the long retrieval delays, it is a logical assumption that Amazon is using magnetic tapes for the storage.
Amazon suggests that the service would be used for archiving and preserving records, media, scientific data, or anything that requires long-term storage. It would work well for off-site backups in general, even for your personal computer, since storage is absurdly cheap and you don’t need to retrieve backups too often.