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Developers pay $0.15 per GB of storage per month and $0.20 per GB of data transferred. That's cheaper than a lot of hosting services.
When you store data with Amazon S3, you assign a unique object key that can later be used to retrieve the data.
Since the Amazon S3 API uses standard REST (XML/HTTP) and SOAP interfaces, S3 applications can be written in Java, Ruby, Perl, C#, PHP or any Internet-development toolkit.
Read more: Amazon S3 - Simple Storage Service
Download Amazon S3 API Docs | Amazon S3 Code Samples
Source: BusinessWeek | TechCrunch