Well, I have written this some time ago during my studies at my Masters, and I finally decided to put this here too. It’s a basic review of what is cloud, how we are seeing it, how are some of the service providers fare against each other and some security issues etc. You may like it or not, so feel free to give any feedback. It will contain many parts so stick with me till the very end :)
This part contains things about what is cloud.
The term “cloud” is used as a metaphor for the Internet, based on the cloud drawing used in the past to represent the telephone network,  and later to depict the Internet in computer network diagrams as an abstraction of the underlying infrastructure it represents. 
Cloud is the definition of a new kind of a SaaS platform for end-users who does not know anything else then the service is provided to them by some means. They can change their services anytime they wish to match their needs, like increasing their server numbers and performance to match the current request on their web site or decreasing them on idle times to decrease their maintenance costs. It’s a service which you don’t have any knowledge on what is the location of your current servers or where exactly your documents are stored. Cloud helps you to match what you have and what you need allowing you to increase or decrease the resources you have anytime you wish with a single click of a button.
Cloud provides services for end-users who does not have a resource to solve (mostly technical) problems without bothering you on how to do or what to do. Simply, it might be considered as an outsourcing. You don’t know how they do it, but when you give it the input you receive the desired output.
Cloud Model is used for both the service providers which they have a profit model based on cloud and also for the consumers of this service which they base their needs or products on the cloud.
As Cloud is a new kind of outsourcing model, services provided are also diverse. However cloud services are mostly based on digital services like (in the most basic way) storing or processing digital data. You might store you data in order to reach it from anywhere on the world by any machine you have including mobile devices. You might also want to store your data for backup purposes on a scheduled basis. You might provide a service that processes your web users request and sends the responses you want to them (an application server). Perhaps you are a publication agency and you want to send thousands of emails to your subscribers per day.
Cloud services are diverse and the number of possible different services are nearly infinite. Amazon provides you services which provides you a remote computer, with the operating system you want in mere minutes, even some of the software you will be using might be pre installed based on your selections.
When we look at different cloud services and service providers, we will notice similar characteristics for all them. These characteristics might be cited as:
- Empowerment of end (service/cloud) users
- Agility to change to your infrastructure based on your needs, on your peak-times, etc.
- Application programming interface (API) accessibility
- Accessibility, device and location independence
- Cost reduction
- Easy maintenance
These characteristics will be detailed in the following chapters of this document.
The term cloud comes from drawings of telephone networks which later will also define Internet too. As cloud is empty and you don’t truly know what it contains, it’s also fitting regarding to the abstraction for end users which cloud models provide.
The actual term cloud borrows from telephony in that telecommunications companies. By switching traffic to balance utilization as they saw fit, they were able to utilize their overall network bandwidth more effectively. The cloud symbol was used to denote the demarcation point between that which was the responsibility of the provider and that which was the responsibility of the user. Cloud computing extends this boundary to cover servers as well as the network infrastructure. 
With Amazon emerging as a powerful company, they found out that they were only using %10 of their resources at a single time. Similar to the telephone networks they might have turned these resources useful to someone else, both internally and externally. They initiated a new product Amazon Web Services (AWS) and released the utility computing part in 2006.
The year 2008 was really a huge leap for cloud computing. In the early days of the year, Eucalyptus became the first open-source, AWS API-compatible platform for deploying private clouds. OpenNebula followed Eucalyptus’ release as an open-source project to deploy private and hybrid clouds and also for federation of clouds. n the same year, efforts were focused on providing QoS guarantees for real-time application to cloud-based infrastructures, in the framework of the IRMOS European Commission-funded project, resulting to a real-time cloud environment. 
In the end 2011, we see a shift towards cloud computing. The number of service providers have increased, creating a competition between service providers which had a positive impact on the current services’ effectiveness and availability. Some companies are also moving their important data centers to private clouds.
 “Writing & Speaking”. Sellsbrothers.com. Retrieved 2010-08-22.
 “The Internet Cloud”. Thestandard.com. Retrieved 2010-08-22.