Once synonymous with software-as-a-service (SaaS, typically pronounced "saz"), cloud computing actually has come to encompass a variety of different types of services. Born out of the so-called "service bureaus" of the 1960s, cloud computing is now sold in a number of different flavors, all ending in "as a service."

The most popular of these services continues to be SaaS. The basic gist of SaaS is that you pay someone to use software. Owned by a provider who grants you a license to use it, this software is almost always accessed over the Internet. The software runs on hardware and operating systems (e.g., Windows, Unix) that are owned, operated and maintained by the SaaS provider. The facility in which this hardware sits is either owned or leased by the provider as well.

Typically under the SaaS model, the provider takes care of everything. Software upgrades, bug fixes, support, Internet connection, hardware operation, power, access and just about anything else needed to keep the software usable is addressed by the provider.

PaaS, or platform-as-a-service, is similar to SaaS, but you own, build or pay someone to build the software that is accessed over the Internet. The operating system and hardware belongs to and is operated by the PaaS provider. The PaaS provider owns or leases the facility in which this hardware resides.

With PaaS you are usually responsible for all things related to the application software, including licensing, support and maintenance. The provider is on the hook to ensure that you can connect to and run your software.

Infrastructure-as-a-service (IaaS) providers supply the Internet connectivity, hardware and facility. They make sure that the foundation upon which the software runs is stable; everything else is in your court.

Clearly, prices vary between these models. When shopping for a service like those mentioned above, organizations need to make an honest assessment of their own IT capabilities and associated costs. Many businesses and public-sector agencies are quite capable of supporting their software in an efficient manner that would facilitate the use of a PaaS or IaaS provider. Others, well, not so much.

Further, when assessing providers, care should be taken to ensure that they have the complete set of skills and experience you are seeking. It is not a given, for example, that a provider well versed with IaaS knows anything about your software. Similarly, a SaaS provider might be a whiz at the application level but weak on infrastructure.

This article is republished with permission from a column that previously appeared in The Honolulu Star Bulletin (www.starbulletin.com) on April 10, 2010.