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Definition: cloud computing

Hardware and software services from a provider on the Internet (the "cloud"). Cloud providers replace in-house operations and are invaluable for companies, no matter their size or applications. Cloud servers can be configured to handle tiny or huge amounts of traffic and expand or contract as needed. For the in-house version of cloud computing, see intranet.

Is Every Internet Function Cloud Computing?
Not exactly. Websites, email, automatic updates, backup, photo storage, streaming, virtually anything over the Internet might be considered cloud computing because the Internet is the biggest cloud there is. However, technically, cloud computing comprises the following two services.

Software Service
Cloud computing started with software as a service (SaaS), which offers online applications on a subscription basis that were previously installed in the user's computer. Salesforce.com was notably one of the first, and the incentive was no more hassle with in-house maintenance. Everything is handled online and managed by the cloud provider.

Hardware Service
Secondly, tech giants such as Amazon, Google, Microsoft and IBM, with years of running huge datacenters, began to rent time on their machines, offering companies both large and small a very viable alternative. Amazon Web Services (AWS) is the largest.

The cloud can eliminate the security, maintenance, network and environmental issues with in-house datacenters. In addition, commercial clouds may meet military standards for natural disasters. See Amazon Web Services, Google App Engine and Windows Azure.

Cloud Computing Features
(Self Service) The customer sets up an account and activates the process from start to finish.

(Scalability) Both users and computer hardware can be easily added and deleted.

(Speed and Reliability) Multiple datacenters and backbones provide fast response times and fault tolerance.

It Started With SaaS (Software as a Service)
After the Web became popular in the late 1990s, for the first time, SaaS providers offered an application to the end user online, eliminating all routine software maintenance. Using this model today, numerous apps run from a Web browser, including email, office suites and routine business applications (CRM, ERP, etc.). Customers pay by the number of users. For the IT department, this was a paradigm shift. However, every solution generates other problems. When data are stored outside the company, there are security and privacy issues.

IaaS (Infrastructure as a Service)
Also called "cloud hosting" and "utility computing," IaaS provides the bare hardware, or the hardware plus a virtual machine (VM), which is one partition in a server shared by many customers. IaaS customers upload all the software, from OS to applications. See virtual machine and software stack.

PaaS (Platform as a Service)
PaaS includes the operating system and database, plus all necessary system software to run applications (the "stack"). With IaaS and PaaS, customers pay by some combination of server size, speed, storage capacity and network time (uploads and downloads). See runtime engine and system software.

FaaS (Function as a Service)
At the most granular level, FaaS customers pay only for the time it takes to execute specific tasks (see serverless computing).

The Virtualization Foundation
Cloud datacenters employ server virtualization, which, among other benefits, allows workloads to be added and removed as self-contained modules. IaaS and PaaS customers require technical skills to configure these functions. It is safe to say that without virtualization having become mainstream in the IT world, cloud computing would not have emerged. See server virtualization and virtual machine.

Private and Hybrid Clouds
Enterprises can create private clouds in their datacenters that employ the same cloud computing infrastructure used on the Internet. The private cloud provides the same flexibility and self-service capabilities, but with control of privacy.

A hybrid cloud is both private and public. If the private cloud is overloaded, applications are activated on the Internet cloud. Extending software and databases from internal servers to a provider's servers and managing both venues from a central console are major issues in cloud computing administration. See fog computing, cloud management system, multicloud, personal cloud, Windows Azure, thin client, cloud storage, colocation, Open Cloud Manifesto and Web application.