As one of the oldest and most popular models of Cloud Computing, Software as a Service (SaaS) is also one of the most familiar to the general public. SaaS has evolved from the earlier software delivery model used by Application Service Providers (ASP). While ASPs used dedicated hardware and software resources tailored to the needs of individual clients, SaaS providers leverage the economies of scale inherent in the cloud in order to deliver more homogeneous applications to a wider user base. Today, many people use freely available web based email and productivity software without even realizing they are SaaS customers. Even the voicemail service provided by your phone company is essentially a SaaS alternative to owning and operating a conventional answering machine. While Infrastructure as a Service offers core services in the form of virtual machines, and Platform as a Service provides an interface for programming applications, SaaS takes the concept a step further by delivering complete applications. End users own and operate their client interface devices as the final service level . These devices can be small footprint software installations, web browsers, or mobile devices. As is the case with voicemail, even a telephone can act as the client layer for Software as a Service.
Since Cloud Computing seeks to deliver information technology resources simply as a service to end users, Software as a Service is the logical limit of its potential. As with other cloud computing models, there is no requirement for hardware acquisition, installation, or maintenance. SaaS clients do not need to utilize any systems administration or development resources either. While SaaS clients may be able select various software options, its defining characteristic is that software development is not needed before an application is deployed to end users. Most services are sold with a monthly or annual fee per user such that the costs are less than enterprise application licensing. SaaS clients value the instant scalability of SaaS as well as the ease of collaboration common to cloud hosted applications.
Like other Cloud Computing services, SaaS clients must overcome the concerns of having their data stored in a third party environment. The SaaS model is unique in that requires business and government entities to entrust both their data and their applications entirely to their cloud providers. Some of these concerns can be alleviated by using a data escrow service in order to ensure continuity in the event that their service provider suffers a technical or business failure. Other potential drawbacks include customer’s complete reliance on secure and stable Internet connections. Users who require uninterrupted access to their applications from remote locations may wish to use their own device host mission critical applications. Finally, client of SaaS applications are limited to minor configuration changes and are unable to customize applications to the extent that clients of other cloud service models are.