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provider and subscribers are working within the company. Cloud servers are built by the IT service
department. he services and computing resources are provided by the company's IT department.
he data will be stored in the data center located on the company's private network. he private
cloud allows the company to have a total control of the data. he company can decide what secu-
rity measures to be enforced on the private cloud. he cloud subscribers are authenticated by the
company.
By establishing a private cloud, a company can take advantage of the lexibility and availability
provided by cloud computing without paying subscription fees to a third-party cloud provider.
Since the data are stored on a private network, the company is less worried about its private data
being exposed to the public. On the other hand, it requires the company to have a group of skilled
technical personnel and adequate computing resources to develop and manage the private cloud.
In a public cloud, the services and computing resources are provided by a third-party cloud
provider. he data center and IT infrastructure used to support cloud computing are developed
and managed by the third-party cloud provider. Some of the well-known ones are Amazon Elastic
Compute Cloud (EC2), IBM Blue Cloud, Microsoft Windows Azure, and so on. Based on the
needs of a cloud subscriber, the third-party cloud provider dynamically provisions computing
resources. Companies or individuals subscribe and pay for cloud services and computing resources.
By subscribing to cloud services and computing resources, a company does not have to develop
its own IT infrastructure to support its e-commerce. Without investing in IT infrastructure, the
company can signiicantly reduce the initial cost and can start its business right away. he draw-
back of a public cloud is that cloud subscribers have no control over where the data are stored. he
data center of a public cloud can store the data anywhere around world. he lack of knowledge
about where the data are stored may cause some concerns about the public cloud. For example, an
educational institution is required to keep the students' privacy. If the student data are stored in
a data center located in a foreign country, it may violate state or federal government regulations.
Also, it is always a concern to place an organization's inancial system entirely on a third party's
public cloud without knowing where the data are stored.
To take advantage of the public cloud and to keep the data safe, a third type of cloud, hybrid
cloud, is accepted by many companies. For many companies, they have the existing IT infrastruc-
ture for their daily business operations. hese companies can keep their inancial systems on their
own private clouds and use the public cloud to support the less sensitive business processes such as
the companies' web applications. On the other hand, by using the hybrid cloud, a company may
end up paying fees for subscribing the services and computing resources to the third-party cloud
provider as well as for developing and managing the private cloud. If the cost of using both the
private cloud and the public cloud is too high, the company may consider the private cloud option.
here are three major types of cloud services: SaaS, IaaS, and PaaS. Recently, the personal
cloud has also become available in cloud computing. A brief introduction of these types of cloud
services is given below.
1.5.1 Software as a Service
his type of cloud service provides application software running on a cloud infrastructure to cloud
subscribers. It allows companies to use web-based application software and pay for the usage of the
software. As subscribers, the companies do not need to manage the IT infrastructure, including
networks, servers, operating systems, and databases, to support the application software. Since
the application software is running on a cloud-based server, the software is accessible through
web browsers. he personal computing devices such as notebook computers or even smart phones
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