Clouds come in many different forms.
Clouds can be both private and public. Public clouds sell their services to anyone on the internet (e.g. Amazon Web services). Private clouds, on the other hand, are proprietary networks or data centres that supply hosted services to a selected number of people – e.g. within a single company.
Whether private or public, the aim of cloud computing is to provide easy access to computing resources and IT services.
Clouds can also be classified according to the different services they offer:
- Infrastructure-as-a-Service (IaaS) - buying access to computing capacity over the internet, such as servers or storage. Also known as utility computing, as it is like buying in a utility service such as gas or electricity. IaaS often employs virtualisation so users can create their own "virtual computer". This means they can specify the applications, software and operating system they want to deploy in the cloud. Advantages are that users don't need to worry about purchasing and running their own hardware but disadvantages include that it can be difficult to package up and run a computer remotely.
- Platform-as-a-service (PaaS) - developing applications that use web-based tools, so they run in a software environment (i.e. a platform) provided by another company.
- Software-as-a-service (SaaS) - using a complete application running on someone else's system. Web-based email and customer service management systems are examples of SaaS.