Ask a dozen people and you'll get a dozen different definitions. In a nutshell, cloud storage is a utility-type service that provides multiple users or "tenants" access to a shared pool of storage capacity, which is accessed over an Internet connection. Storage clouds are scalable, and they can easily expand or contract according to customer needs.

The public cloud is a pay-per-use storage utility. All components sit outside of the customer's firewall in a shared infrastructure that is logically partitioned, multitenant and accessed over a secure Internet connection.

Public cloud storage providers, such as Amazon.com Inc. with its Simple Storage Service, typically charge a monthly usage fee per gigabyte of storage plus an additional bandwidth fee for transferring data to and from the cloud. Public cloud customers require no physical storage hardware or any special in-house technical expertise.

Rather, the cloud storage service provider manages the storage infrastructure, pooling its capacity to accommodate the needs of multiple customers. Users typically access their publicly stored data via an Internet connection.