【導讀】“云計算”是一個相對較新詞語，是建立在對虛擬化，分布式計算，效用計算，以及最近的網(wǎng)絡，網(wǎng)絡和軟件服務數(shù)十年的研究的基礎之上產生的。權，按需服務，以及其他許多東西總成本。本文討論了“云”計算，它試圖解決的問。題和相關研究課題，以及“云”技術在今日的實施運用。“云計算”是未來信息技術服務和產品順應時代發(fā)展的下一步演化。云計算前身的出現(xiàn)距今已經有一段時間了[例如，AEC08，Con08，F(xiàn)os04，Glo08，自2020年以來北卡羅來納州立大學已經在進行VCL的生。產使用，適用于動態(tài)的載體實施任何電流云計算的解決方案。如今，幾乎任何業(yè)務或重大活動都使用或依賴于IT和IT服務的某種形式。結果的能力，即信息收集和使用出處。有跡象表明，同樣還有非常重要。這些包括可靠性及組件和服務，服務，安全成本，總擁有成本，規(guī)模經。程代表了系統(tǒng)活動信息和計算所發(fā)生的一系列協(xié)助解決問題的過程。的一部分[Alt07a，Bat07]基于開普勒方程的執(zhí)行情況。圖1是基于開普勒方程

　　

【正文】 to individual and aggregated putational and other resources, autonomics, ability to group resources from potentially different ―clouds‖ to deliver workflow results, appropriate level of security and privacy, etc. . Virtualization Virtualization is another very useful concept. It allows abstraction and isolation of lowerlevel functionalities and underlying hardware. This enables portability of higherlevel functions and sharing and/or aggregation of the physical resources. The virtualization concept has been around in some form since 1960s (., in IBM mainframe systems). Since then, the concept has matured considerably and it has been applied to all aspects of puting – memory, storage, processors, software, works, as well as services that IT offers. It is the bination of the growing needs and the recent advances in the IT architectures and solutions that is now bringing the virtualization to the true modity level. Virtualization, through its economy of scale, and its ability to offer very advanced and plex IT services at a reasonable cost, is poised to bee, along with wireless and highly distributed and pervasive puting devices, such as sensors and personal cellbased access devices, the driving technology behind the next waive in IT growth [Vou08b]. Not surprisingly there are dozens of virtualization products, and a number of small and large panies that make them. Some examples in the operating systems and 4 software applications space are VMware1, Xen an open source Linuxbased product developed by XenSource2, and Microsoft virtualization products3, to mention a few. Major IT players have also shown a renewed interest in the technology4,5,6,7,8,9 [IBM06, Sun06]. Classical storage players such as EMC10, NetApp11, IBM12 and Hitachi13 have not been standing still either. In addition, the work virtualization market is teeming with activity. . Users The most important Cloud entity, and the principal quality driver and constraining influence is, of course, the user. The value of solutions depends very much on the view it has of its enduser requirements and user categories. Figure 2. Cloud user hierarchy 1 2 3 4 webamp。me=escallout 5 ., 6 ., m and 7 ., en/Processors/ProductInformation/0,30_118_8826_14287, 8 9 10 11 12 13 Figure 2 illustrates four broad sets of nonexclusive user categories: System or Cyberinfrastructure (CI) developers, developers (authors) of different ponent services and underlying applications, technology and domain personnel that integrates basic services into posite services and their orchestrations (workflows) and delivers those to endusers, and finally users of simple and posite services. User categories also include domain specific groups, and indirect users such as stakeholders, policy makers, and so on. Functional and usability requirements derive, in 5 most part, directly from the user profiles. An example, and a discussion, of user categories appropriate in the educational domain can be found in [Vou99]. Specifically, a successful ―cloud‖ in that domain the K20 and continuing education would be expected to: a. Support large numbers of users that range from very naive to very sophisticated (millions of student contact hours per year). b. Support construction and delivery of content and curricula for these users. For that, the system needs to provide support and tools for thousands of instructors, teachers, professors, and others that serve the students. c. Generate adequate content diversity, quality, and range. This may require many hundreds of authors. d. Be reliable and costeffective to operate and maintain. The effort to maintain the system should be relatively small, although introduction of new paradigms and solutions may require a considerable startup development effort. . Developers Cyber Infrastructure developers who are responsible for development and maintenance of the Cloud framework. They develop and integrate system hardware, storage, works, interfaces, administration and management software, munications and scheduling algorithms, services authoring tools, workflow generation and resource access algorithms and software, and so on. They must be experts in specialized areas such as works, putational hardware, storage, lowlevel middleware, operating systems imaging, and similar. In addition to innovation and development of new ―cloud‖ functionalities, they also are responsible for keeping the plexity of the framework away from the higherlevel users through judicious abstraction, layering and middleware. One of the lessons learned from, for example, ―grid‖ puting efforts is that the plexity of the underlying infrastructure and middlware can be daunting, and if exposed can impact wider adoption of a solution. . Authors Service authors are developers of individual baseline ―images‖ and services that may be used directly, or may be integrated into more plex service aggregates and workflows by service provisioning and integration experts. In the context of the VCL 6 technology, an ―image‖ is a tangible abstraction of the software stack [Ave07, Vou08a]. It incorporates a) any baseline operating system, and if virtualization is needed for scalability, a hypervisor layer, b) any desired middleware or application that runs on that operating system, and c) any enduser access solution that is appropriate (., ssh, web, RDP, VNC, etc.). Images can be loaded on ―baremetal‖, or into an operating system/application virtual environment of choice. When a user has the right to create an image, that user usually starts with a ―NoApp‖ or a baseline image (., Win XP or Linux) and extends it with his/her applications. Similarly, when an author