云计算的未来应高度考虑在任何行业的企业。云计算的能够完全适应任何一个行业的可能性正在 慢慢开始出现。如果一个企业不考虑在云计算时代的未来，面临的挑战以及云计算的优势可能无法得 到合理和充分利用。

附外文文献原文Cloud Computing - The Emerging Technology of Computing

ABSTRACT：Cloud computing is a general term for anything that involves delivering hosted services over the Internet. These services are broadly pided into three categories: Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS) and Software-as-a-Service (SaaS). The name cloud computing was inspired by the cloud symbol that's often used to represent the Internet in flowcharts and diagrams. It is the 5th generation of computing after mainframe, personal computer, client server computing and the web. In this certain application, limitation and future scope of this technology was discussed.

KEY WORDS: Cloud computing, IaaS(Infrastructure-as-a-Service), PaaS(Platform-as-a-Service), SaaS (Software-as-a-Service)

1 Introduction

A cloud service has three distinct characteristics that differentiate it from traditional hosting. It is sold on demand, typically by the minute or the hour; it is elastic -- a user can have as much or as little of a service as they want at any given time; and the service is fully managed by the provider (the consumer needs nothing but a personal computer and Internet access). Significant innovations in virtualization and distributed computing, as well as improved access to high- speed Internet and a weak economy, have accelerated interest in cloud computing.

A cloud can be private or public. A public cloud sells services to anyone on the Internet. (Currently, Amazon Web Services is the largest public cloud provider.) A private cloud is a proprietary network or a data center that supplies hosted services to a limited number of people. When a service provider uses public cloud resources to create their private cloud, the result is called a virtual private cloud. Private or public, the goal of cloud computing is to provide easy, scalable access to computing resources and IT services[1].

Infrastructure-as-a-Service like Amazon Web Services provides virtual server instances with unique IP addresses and blocks of storage on demand. Customers use the provider's application program interface (API) to start, stop, access and configure their virtual servers and storage. In the enterprise, cloud computing allows a company to pay for only as much capacity as is needed, and bring more online as soon as required.

Platform-as-a-service in the cloud is defined as a set of software and product development tools hosted on the provider's infrastructure. Developers create applications on the provider's platform over the Internet. PaaS providers may use APIs, website portals or gateway software installed on the customer's computer. Force.com, (an outgrowth of Salesforce.com) and Google Apps are examples of PaaS. Developers need to know that currently, there are not standards for interoperability or data portability in the cloud. Some providers will not allow software created by their customers to be moved off the provider's platform.

In the software-as-a-service cloud model, the vendor supplies the hardware infrastructure, the software product and interacts with the user through a front-end portal. SaaS is a very broad market. Services can be

anything from Web-based email to inventory control and database processing. Because the service provider hosts both the application and the data, the end user is free to use the service from anywhere.

2 Benefits of Cloud Computing

(a) Minimized Capital expenditure

(b) Location and Device independence

(c) Utilization and efficiency improvement

(d) Very high Scalability

(e) High Computing power

A. VendorPerspective

Easier for application vendors to reach new customers

(a) Lowest cost way of delivering and supporting applications