Cloud computing can be defned as a pool of virtualised computing resources that allows users to gain access to applications and data in a web-based environment on demand.
Cloud computing a modality of computing characterized by on demand availability of resources in a dynamic and scalable fashion. The term resource here could be used to represent infrastructure, platforms, software, services, or storage. The cloud
provider is responsible to make the needed resources available on demand to the cloud users. It is the responsibility of the cloud provider to manage its resources in an efficient way so that the user needs can be met when needed at the desired Quality of Service (QoS) level. For example, an infrastructure cloud offers computing infrastructure, typically in the form of virtual machines allocated to physical
servers, as needed by its users. Cloud users are charged, in most cases, by how much resources they consume.
Cloud architectures can be broadly categorised into:
Infrastructure as a Service (IaaS) is the foundation of cloud services. It provides clients with access to server hardware, storage, bandwidth and other fundamental computing resources. For example, Amazon EC2 allows individuals and businesses to rent machines preconfgured with selected operating systems on which to run their own applications.
Platform as a Service (PaaS) builds upon IaaS and provides clients with access to the basic operating software and optional services to develop and use software applications (eg database access and payment service) without the need to buy and manage the underlying computing infrastructure. For example, Google App
Engine allows clients to run their web applications
Software as a Service (SaaS), builds upon the underlying IaaS and PaaS provides clients with integrated access to software applications. For example, Oracle SaaS Platform allows independent software vendors to build, deploy and manage SaaS and cloud-based applications using a licensing economic model. Here, users
purchase a license and support for components of the Oracle SaaS Platform on a monthly basis.
Benefits
Cloud computing provides a scalable online environment which facilitates the ability to handle an increased volume of work without impacting on the performance of the
system. Cloud computing also offers signifcant computing capability and economy of scale that might not otherwise be affordable to businesses, especially small and medium enterprises (SMEs) that may not have the fnancial and human resources
to invest in IT infrastructure. Advantages include:
• Capital costs—SMEs can provide unique services using large-scale resources
from cloud service providers and ‘add or remove capacity from their IT infrastructure
to meet peak or fuctuating service demands while paying only for the actual capacity used’ (Sotomayor et al. 2009: 14) on a ‘pay-as-you-go’ economic model.
• Running costs—it can also be signifcantly cheaper to rent added server space for a
few hours at a time rather than maintain proprietary servers. Rental prices for
Amazon Elastic Compute Cloud (EC2), for example, are between US$0.10–1.00
an hour. Businesses do not have to worry about upgrading their resources whenever
a new version of the application is available. Businesses can also base their
services in the data centres of bigger enterprises or host their IT infrastructure
in locations offering the lowest cost.
• No need to provision for peak loads: If cloud computing resources are used, the responsibility to support
• Time to market : Because users of cloud computing resources do not need to procure, install, and test all the infrastructure including middleware and applications in many cases, they can be up and running invery little time.
• Consistent performance and availability: When services are provided by the cloud under strict SLAs that are specific on response time and availability, users do
not need to worry so much about maintaining adequate levels for these metrics. This burden is shifted to the cloud, which, by virtue of managing a typically large infrastructure may be able to autonomically shift resources (e.g., virtual machines) to keep up with varying and unpredictable workloads.
Advantages of using cloud services can also go beyond cost savings as cloud computing allows clients to:
• avoid the expense and time-consuming task of installing and maintaining hardware infrastructure and software applications; and
• allow for the rapid provisioning and use of services to clients by optimising their
IT infrastructure
more from Wikipedia http://en.wikipedia.org/wiki/Cloud_computing
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