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cloud computing

What is cloud computing? To understand cloud computing, examine public, private and hybrid cloud, as well as PaaS, SaaS and IaaS cloud models.

Cloud computing is a general term for the delivery of hosted services over the Internet. Cloud computing enables companies to consume compute as a utility – similar to electricity or a telephone service – rather than building and maintaining computing infrastructures.

Cloud computing promises several attractive benefits for businesses and end users. Three of the main benefits of cloud computing include:

• Self-service provisioning: End users can spin up computing resources for almost any type of workload, on-demand, and without direct intervention from IT administrators.
• Elasticity: Companies can scale up as computing needs increase and then scale down again as demands decrease.
• Pay per use: Computing resources are measured at a granular level, allowing users to pay only for the resources and workloads they use.

To define cloud computing, it's important to look at all three pillars of cloud. A cloud is classified as private, public or hybrid. A private cloud is created within a business' data center and provides services to internal users. This model offers cloud's versatility, while preserving management, control and security.

In the public cloud model, a third-party provider delivers the cloud service over the Internet. Three distinct characteristics differentiate public cloud computing from in-house or hosted data centers.

First, public cloud is sold on-demand, typically by the minute or the hour. Customers only pay for the computing resources they use, such as CPU cycles, storage or network bandwidth. Second, cloud computing is highly elastic, adding or subtracting resources on-demand. Leading public cloud providers include Amazon Web Services (AWS), Microsoft Azure, IBM/SoftLayer and Google Compute Engine.

Hybrid cloud is a combination of public cloud services and on-premises private cloud – with orchestration and automation between the two. Companies can run mission-critical workloads or sensitive applications on the private cloud while using the public cloud for "bursty" workloads that must scale on-demand. The goal of hybrid cloud is to create a unified, automated, scalable environment.

Although the cloud computing definition has changed over time, cloud computing has always been divided into three broad service categories: infrastructure as a service (IaaS), platform as a service (PaaS) and software as service (SaaS).

IaaS providers such as AWS supply a virtual server instance and storage, as well as application program interfaces (APIs) that let users migrate workloads to a virtual machine (VM). Users have an allocated storage capacity and start, stop, access and configure the VM and storage as desired. IaaS providers offer small, medium, large, extra-large, and memory- or compute-optimized instances, in addition to customized instances, for various workload needs.

In the PaaS model, providers host development tools on their infrastructures. Users access those tools over the Internet using APIs, Web portals or gateway software. PaaS is used for general software development, such as Java or Perl, and to create custom applications. A PaaS provider often hosts the software after it's developed. Common PaaS providers include's, Amazon Elastic Beanstalk and GoogleApps.

SaaS is the cloud software distribution model that delivers services over the Internet; these are often called Web services. Microsoft Office 365 is a SaaS offering for productivity software and email services. Users can access SaaS applications and services from any location using a computer or mobile device that has Internet access.  

See also: hybrid cloud, cloud backup

This was first published in December 2010

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