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"Cloud Computing" can be simply defined is "information technology services that can be used or accessed by customers through the Internet or bias as well". The words "Cloud" itself refers to the symbol of a cloud in the IT world is used to describe the Internet (Internet cloud). However not all existing services on the Internet can be categorized as Cloud Computing, there are at least several requirements that must be met:

1. Service is "On Demand", users can subscribe to just that he needs it, and pay only for what they use it. Suppose an Internet service provider providing a 5 different options or packages internet and the user simply takes a package of internet, the user only pays any packets captured.

2. Service is elastic / scalable, where users can add or reduce the type and capacity of services they want at any time and the system is always able to accommodate those changes. Suppose the user's Internet subscription in the bandwitchnya 512Kb / s and want to add speed to 512Kb / s then the user asks to call customer service and customer service additions bandwitch respond by changing bandwitc to 1Mb / s.

3. Services are fully managed by the provider / provider, the user is only required by the personal computer / laptop plus an Internet connection.

In terms of individual types of services, Cloud Computing, divided into 3 types of services, namely: Software as a Service (SaaS), Platform as a Service (PaaS) and Infrastructure as a Service (IaaS).

· Software as a Service SaaS is the Cloud Computing services are the most popular first. Software as a Service is a further evolution of the concept of ASP (Application Service Provider). As the name implies, SaaS makes it easy for users to be able to utilize the software with a subscription. So it does not need to spend a good investment for in-house development or purchase of a license. By subscription via the web, users can directly use the various features provided by the service provider. It's just that the concept of SaaS, the customer does not have complete control over their lease applications. Only the application features that have been provided by the providers that can be rented by the customer. And since SaaS application architecture is multi tenant, forcing providers to only provide the features of a general nature, not specific to the needs of specific users. However, customization does not necessarily prohibited, even if only for a limited scale and function. But with the development of markets and advances in programming technology, the limitations must be reduced in a time not too long. For an example of SaaS services, of course we must mention an online CRM service Salesforce.com--a dikomandai Marc Benioff and has become an icon of this SaaS. Additionally Zoho.com, with a very affordable price, providing SaaS services are quite diverse, ranging from services like Google Docs word processor, project management, to online invoicing. Online accounting service is also available, as given by Xero.com and much more. IBM with its Lotuslive.com can serve as an example for SaaS services in the areas of collaboration / unified communication. Unfortunately for the domestic market itself, as I have to say in a previous article, are still very few are willing to invest to provide this service SaaS.

· Platform as a Service (PaaS) that is As the name suggests, PaaS is a service that provides ready-made modules that can be used to develop an application, which of course can only run on that platform. As well as service SaaS, PaaS users do not have control over basic computing resources such as memory, storage, processing power, etc., which are all governed by the service provider. Pioneers in this area is Google AppEngine, which provides various tools for developing applications on the platform of Google, using the programming language Python and Django. Then Salesforce also provides services through Force.com PaaS, providing modules to develop applications on a platform that uses Salesforce Apex language. And maybe that rarely do we know that Facebook can also be considered to provide a service PaaS, which allows us to create applications on top.

· Infrastructure as a Service (IaaS) IaaS is located one level lower than PaaS. It is a service that "rent" the basic information technology resources, which includes media storage, processing power, memory, operating system, network capacity and others, which can be used by the tenant to run the applications it has. Business model similar to the data center providers that rent out space for co-location, but this is more to the micro level. Tenants do not need to know, with what machine and how IaaS providers to provide services. Importantly, their request on the basis of information technology resources can be met. The fundamental difference with current data center services is IaaS enables customers to do the addition / reduction of capacity in a flexible and automated. One of the pioneers in providing IaaS is that Amazon.com launched Amazon EC2 (Elastic Computing Cloud). Amazon's EC2 service provides a wide selection of rental starts the CPU, storage media, equipped with the operating system and application development platform that can be rented hourly calculations. For in their own country, the plan there are some providers that will provide a similar service starting this summer. whereas for the range of services, divided into 3 namely Public Cloud, Private Cloud and Hybrid Cloud.

1. Public Cloud's as simple as its name, type of cloud is dedicated to the public by the service provider. The services I mentioned earlier can be used as examples of public cloud in

2. Where a Private Cloud infrastructure cloud services, operated only for a particular organization. Infrastructure cloud could have been managed by the organization or by third parties. The location can be on-site or off-site. Usually organizations with large scale are able to have / manage this private cloud.

3. Hybrid Cloud For this type, the available cloud infrastructure is composed of two or more cloud infrastructure (private, community, or public). Where the entity even though they still stand on their own, but connected by a technology / mechanism that enables data and application portability between the cloud it. For example, load balancing mechanism that antarcloud, so that the allocation of resources can be maintained at optimal levels. So little explanation of cloud models are abstracted from NIST. However, as recognized by this institution, and limits the definition of Cloud Computing itself is still looking for forms and standards. Where will pasarlah that will determine which model will survive and which model will die. But all agreed that cloud computing will be the future of the computing world. Even the prestigious research institute Gartner Group has stated that Cloud Computing is a discourse that is not to be missed by all stakeholders in the IT world, began at this time and in some future time.

Cloud Computing is a mechanism that allows us to "hire" of information technology resources (software, processing power, storage, etc.) through the Internet and exploit according to our needs and pay that is used by us alone. With this concept, the more people who can have access to and use of these resources, because they do not have to make massive investments. Especially in economic conditions like now, each organization will think long to issue an additional investment in the IT side.