Cloud computing refers to the provision of computational resources on demand via a computer network. Because the cloud is the underlying delivery mechanism, cloud based applications and services may support any type of software application or service in use today. Before the advent of computer networks, both data and software were stored and processed on or near the computer. The development of Local Area Networks LAN allowed for a tiered architecture in which multiple CPUs and storage devices may be organized to increase the performance of the entire system. LANs were widely deployed in corporate environments in the 1990's, and are notable for vendor specific connectivity limitations. These limitations gave rise to the marketing term "Islands of Information" which was widely used within the computing industry. The widespread implementation of the TCP/IP protocol stack and the subsequent popularization of the web has lead to multi-vendor networks that are no longer limited by company walls.
Cloud computing fundamentally allows for a functional separation between the resources used and the user's computer. The computing resources may or may not reside outside the local network, for example in an internet connected datacenter. What is important to the individual user is that they 'simply work'. This separation between the resources used and the user's computer also has allowed for the development of new business models. All of the development and maintenance tasks involved in provisioning the application are performed by the service provider. The user's computer may contain very little software or data (perhaps a minimal operating system and web browser only), serving as little more than a display terminal for processes occurring on a network of computers far away. Consumers now routinely use data intensive applications driven by cloud technology which were previously unavailable due to cost and deployment complexity. In many companies employees and company departments are bringing a flood of consumer technology into the workplace and this raises legal compliance and security concerns for the corporation.
A common shorthand for a provided cloud computing service (or even an aggregation of all existing cloud services) is "The Cloud". The most common analogy to explain cloud computing is that of public utilities such as electricity, gas, and water. Just as centralized and standardized utilities free individuals from the difficulties of generating electricity or pumping water, cloud computing frees users from certain hardware and software installation and maintenance tasks through the use of simpler hardware that accesses a vast network of computing resources (processors, hard drives, etc.). The sharing of resources reduces the cost to individuals.
The phrase “cloud computing” originated from the cloud symbol that is usually used by flow charts and diagrams to symbolize the internet. The principle behind the cloud is that any computer connected to the internet is connected to the same pool of computing power, applications, and files. Users can store and access personal files such as music, pictures, videos, and bookmarks or play games or use productivity applications on a remote server rather than physically carrying around a storage medium such as a DVD or thumb drive. Almost all users of the internet may be using a form of cloud computing though few realize it. Those who use web-based email such as Gmail, Hotmail, Yahoo, a Company owned email, or even an e-mail client program such as Outlook, Evolution, Mozilla Thunderbird or Entourage are making use of cloud email servers. Hence, desktop applications which connect to cloud email would be considered cloud applications.
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