Cloud computing refers to the provision of computational resources on demand via a network. Cloud computing can be compared to the supply of electricity and gas, or the provision of telephone, television and postal services. All of these services are presented to the users in a simple way that is easy to understand without the users needing to know how the services are provided. This simplified view is called an abstraction. Similarly, cloud computing offers computer application developers and users an abstract view of services that simplifies and ignores much of the details and inner workings. A provider's offering of abstracted Internet services is often called The Cloud
How cloud computing works
When a user accesses the cloud for a popular website, many things can happen. The user's IP for example can be used to establish where the user is located (geolocation). DNS services can then direct the user to a cluster of servers that are close to the user so the site can be accessed rapidly and in their local language. The user doesn't login to a server, but they login to the service they are using by obtaining a session id and/or a cookie which is stored in theirbrowser.
What the user sees in the browser will usually come from a cluster of web servers. The webservers run software which presents the user with an interface which is used to collect commands or instructions from the user (the clicks, typing, uploads etc.) These commands are then interpreted by webservers or processed by application servers. Information is then stored on or retrieved from the database servers or file servers and the user is then presented with an updated page. The data across the multiple servers is synchronised around the world for rapid global access and also to prevent data loss.
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