According to the National Institute of Standards and Technology (NIST), there are 5 essential characteristics of cloud computing.
On-demand self-service. This is where you can provision computing capabilities based on your needs. Our needs may change from time to time. This is why it’s called “on-demand”. It’s based on your needs. The cool thing is that, all these provisioning processes don’t need human intervention!
Broad network access. By using cloud, you have the option on whether to burden the end users laptop or in another word, thin or thick client. Thin client is where users have to download a small size file and they can access to all the resources and features available. For thick client, users will have to download a big size of files to their workstations before using the features. In another word, it’s about how much you rely on the cloud and workstation.
Resource pooling. This is another cool thing about cloud computing. Resource pooling is about assigning computing resources to multiple customers dynamically. It is something that can change from time to time based on users demands.
Rapid elasticity. Imagine you are hosting a web site and your average hit per day is 100. Suddenly, you are launching a project and for a particular day, a lot of users will be signing in online at the same time. Your hit for that particular time may rise to 10,000 in a day. For this type of scenario, during a normal day, the cloud will assign you let’s say, 1 server and during peak time, it will rise to 5 servers and back to 1 server during normal hour. The best thing is that, you only pay for how much you use! If you are hosting it yourself, you’ll need to purchase 5 servers to prepare for the peak hours which only will occur once in a blue moon. During the rest of the time, the other 4 servers will just sit there doing nothing. Waste of resources.
Measured service. Since cloud is a pay-as-you-go type, you will be charged based on the amount of resources you use only. Cloud provides usage metering.
Adapted from http://www.beyourfuture.net/2011/09/29/the-5-essential-characteristics-of-cloud-computing/.