When you think of Amazon.com, you probably think of an online site that has decent prices on books, music, toys, and electronics. But if Amazon gets its way, IT professionals will think of Amazon.com as the key storage infrastructure for their Web-based development.

Why? Well, two weeks ago Amazon.com launched Simple Storage Service (S3), a Web-based storage service for Web-application developers (see http://www.amazon.com/s3 ). S3 leverages the storage services that Amazon provides for its own Web sites, giving developers that purchase S3 a reliable and well-tested infrastructure.

S3 uses standard API sets such as Representational State Transfer (REST) and Simple Object Access Protocol (SOAP), and the default download protocol is HTTP. S3 also supports the BitTorrent protocol, to enable broader Web-application distribution. A developer can create storage objects ranging in size from 1 byte to 5GB, with each object containing metadata and object data. You can also create storage objects by defining the metadata. For example, you might want to add a customer-number tag to the metadata.

Because security is a high priority on most developers' lists, S3 supports Amazon Web Services authentication, and each storage object has an ACL to protect your private data. The authentication also permits anonymous access to your data, but the developer has complete control over how and when access is granted. Both individuals and groups of users can access data, although currently only Amazon-defined groups are supported. According to Amazon, though, S3 users will eventually be able to define their own groups.

I looked through S3's developer documentation and found its explanation of the S3 service to be straightforward. Any developer with SOAP or REST experience should have little trouble integrating S3 storage into Web-based applications. You can find the complete developer guide at http://s3.amazonaws.com/doc/s3-developer-guide/index.html .

One issue that might be problematic is the service's cost. The storage fee is $.15 per gigabyte-month (or the storage used per month; the developer guide provides a complete set of equations defining pricing). However, there's also a $.20 per gigabyte transfer fee, which means that an active Web site using this service could be spending hundreds, if not thousands of dollars per month paying for the bandwidth usage generated by Web-site traffic. Active sites could also run up a hefty bill if BitTorrent support is made practical because users would be transferring very large files to and from the site via BitTorrent.

As other vendors enter this market (look for Google, MSN, AOL, and Yahoo!), users will ultimately define success. But competition could also reduce the pricing of Amazon's online storage service, which at this time seems to be S3's Achilles' heel.