Cloud computing is Internet based development and use of computer technology. The cloud is a metaphor for the Internet and is an abstraction for the complex infrastructure it conceals. It is a style of computing where IT-related capabilities are provided “as a service”, allowing users to access technology-enabled services from the Internet without knowledge of, expertise with, or control over the technology infrastructure that supports them.

As of now Cloud computing can be considered to implement the following ideas :

1. Utility computing – which was first suggested by John McCarthy in 1961, where computing is viewed as a public utility.
2. Cluster computing -  which views a group of linked computers as a single virtual computer for high-performance computing (HPC), or
3. Grid computing – where the linked computers tend to be geographically distributed to solve a common problem.

Cloud computing landscape

Cloud Computing diagram

Linux and Open source in the cloud

Linux and open source community contribute in three different ways to the concept of computing within a cloud. They are as follows :

1. SaaS
2. PaaS and
3. IaaS

[ Source : Cloud computing with Linux by M.Tim Jones, Consultant Engineer at Emulex Corp. ]