Cloud computing made it possible for small scale businesses to enjoy benefits like mail servers, storage systems etc., without any physical infrastructure. According to wikipedia cloud computing is defined as follows:

“Cloud computing is a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications and services) that can be rapidly provisioned and released with minimal management effort”.

On demand availability of resources, flexibility, scalability, efficiency, economical are few characteristics of cloud computing services. Cloud computing services are provided according to different service models.

Software as a Service(SaaS):

In this model, users gain access to a specific application or service. Users access this application only when needed and pay as per use. The software is installed by the cloud providers. Cloud users access the software from cloud clients. This makes it convenient for the users to use the application.

Platform as a Service(PaaS):

This model provides users an environment to develop and run applications without any software and hardware constraints. Both hardware and software resources are allocated automatically.

Infrastructure as a Service(IaaS):

This model provides users virtual machines along with many other resources like servers, storage, load balancer etc., for installing operating systems and deploying applications in the cloud infrastructure. Users are charged depending upon the resources allocated and consumed.

Hope this information helps you in choosing the right service model depending upon your requirement. Now, need not buy physical infrastructure for short term projects, instead you can choose from the above and pay only for the amount of resources utilized.