The basic idea of cloud computing is centralized upon certain models and services. These things develop the building blocks for the requirements involved for the use of cloud computing.

These services and models work behind the scene making the cloud computing feasible and accessible for the users. Cloud computing mainly concentrate on two models:

·         Deployment Models

·        Service Models  

Deployment Models: 

Deployment models are characterized by the fact of access for the cloud (type of access) i.e. “how the cloud is located?” Cloud system mainly have four categorization for access:

·        Public

·        Private

·         Hybrid

·         Community

Public Cloud:

The public cloud allowed systems and services to be accessible by the user in a common ground i.e. it is publicly accessed by all its users .Public cloud may be less secure because of its openness e.g. e- mail. 

Private cloud:

Private cloud allowed system and services to be shared and accessible within an organization. It offers increased security because of its private nature. 

Community Cloud:

The community cloud allows systems and services to be accessible by the group of organizations. 

Hybrid Cloud

The Hybrid cloud is mixture of public and private cloud. However, the critical activities are performed using private cloud while the non-critical activities are performed using public cloud. 

Service Models: 

Service models are also known as the levels of cloud computing. Service models are reference models on which the cloud computing is based. These can be categorized into three based services models.

These are 3 pillars of cloud computing:

1.       Infrastructure as a Service (IaaS)

2.      Platform as a Service (PaaS)

3.      Software as a service (SaaS)

Note: There are many other service models all of which can take the form like XaaS i.e. Anything as a Service. This can be Network as a Service, Business as a Service, Identity as a service, Database as a service or Strategy as a service 

The IaaS (Infrastructure as a Service) is the most common basic level of service. Each of the service models make use of the underlying service model, i.e. inherits the security and management mechanism from the underlying models.

IaaS (Infrastructure as a service):

These services provide access to fundamental services like physical machines, virtual machines, virtual storage etc. It means you're buying access to raw computing hardware over the Net, such as servers or storage. Since you buy what you need and pay-as-you-go, this is often referred to as utility computing. Ordinary web hosting is a simple example of IaaS: you pay a monthly subscription or a per-megabyte/gigabyte fee to have a hosting company serve up files for your website from their servers.

PaaS(Platform as a Service):

These services provide the runtime environment for applications, development and deployment tools etc. It means you develop applications using Web-based tools so they run on systems software and hardware provided by another company. So, for example, you might develop your own ecommerce website but have the whole thing, including the shopping cart, checkout, and payment mechanism running on a merchant's server. Force.com (from salesforce.com) and the Google App Engine are examples of PaaS. 

SaaS(Software as a Service)

This model allows to use software applications as a service to the end users. It means you use a complete application running on someone else's system. Web-based email and Google Documents are perhaps the best-known examples. Zoho is another well-known SaaS provider offering a variety of office applications online.