Cloud computing has been an attractive proposition both for the CFO and the CTO of an enterprise primarily due its ease of usage. This has been achieved by large data center service vendors or now better known as cloud service vendors again primarily due to their scale of operations. Google, Amazon, Microsoft, and a few others have been the key players apart from open source Hadoop built around the Apache ecosystem
As shown in Figure the cloud service offerings from these vendors can broadly be classified into three major streams: the Infrastructure as a Service (IaaS), the Platform as a Service (PaaS), and the Software as a Service (SaaS). While IT managers and system administrators preferred IaaS as offered by Amazon for many of their virtualized IT needs, the programmers preferred PaaS offerings like Google AppEngine (Java/Python programming) or Microsoft Azure (.Net programming).
Users of large-scale enterprise software invariably found that if they had been using the cloud, it was because their usage of the specific software package was available as a service—it was, in essence, a SaaS offering. Salesforce.com was an exemplary SaaS offering on the Internet.
From a technology viewpoint, as of today, the IaaS type of cloud offerings have been the most successful and widespread in usage. However, the potential of PaaS has been high: All new cloud-oriented application development initiatives are based on the PaaS model. The significant impact of enterprises leveraging IaaS and PaaS has been in the form of services whose usage is representative of SaaS on the Cloud. Be it search (Google/Yahoo/Bing, etc.) or email (Gmail/Yahoomail/Hotmail, etc.) or social networking (Facebook/ Twitter/Orkut, etc.), most users are unaware that much of their on-line
activities has been supported in one form or the other by the cloud.
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