paper title ：
Above the Clouds: A berkeley View of Cloud Computing
1、云计算对IT业带来的改变
① making software even more attractive as a service
② shaping the way IT hardware is design and puchased
另外， ① 有创新想法的开发者不再需要大笔的资金来购买部署其服务器的硬件，也不需要支付大笔的钱来供给运维人员
② 数量驱动（这个翻译不知道怎么弄比较合适 batch-driven）的公司可以更快地获得效益
2、云计算的定义
Cloud computing refers to both the application delivered as service over the Internet and the hardware and system software in the datacenters that provide those service.
红色的部分被称为SaaS，绿色的部分被称为“Cloud”。
3、公共云 VS 私有云
When a Cloud is made available in a pay-as-you-go maner to the general public, we call it a Public Cloud; the service being sold is Utility Computing.
We use the term Private Cloud to refer to internal datacenters of a business or other organization, not made available to the general public.
4、私有云其实不算在云计算中？
Cloud Computing is the sum of SaaS and Utility Computing, but does not include Private Cloud.
让我们回顾一下这两个词出现的地方，
SaaS -> application delivered as service over the Internet
Utility Computing -> the service being sold on Public Cloud
所以，可以理解为云计算是在基于Internet（而不是intranet）并且在公共云（是对general public开放的）上提供的软件服务。
5、SaaS的使用者、提供者 以及 Cloud的使用者、提供者之间的关系
SaaS User就是终端用户（end user），就是一般的网站会员、访问者等。而SaaS的提供者（即，Cloud的使用者）一般是服务的提供者，即网站的建设者。而Cloud Provider就是类似Google、 Amazon、 Microsoft之类的云服务供应企业。
6、从硬件的观点看，云计算会导致IT行业的三个新变化。
① The illusion of infinite computing resources available on demand, there by eliminating the need for Cloud Computing users to plan for ahead for provisioning.
② allow companies to start small and increase hardware resources only when there is an increase in their needs.
③ the ability to pay for use of computing resources on a short-term basis as needed (e.g. processors by the hour and storage by the day) and release them as needed.
7、几个减少成本的因素：
electricity, network bandwidth, operations, software and hardware
8、Cloud Computing可以省钱
Cloud Computing could offer service below the costs of a medium-sized datacenter and yet still make a good profit.
9、虚拟化的必要性
Any application needs a model of computation, a model of storage , and a model of communication.
为了使云计算满足弹性 (elasticity) 以及可以无限扩展（illusion of infinite capacity）的需求，以上的这些model都必须虚拟化以隐藏它们实现的细节。
基于上述原因，不同的通用计算提供者（utility computing offering） will be distinguished based on the level of abstraction presented to the programer and the level of management of the resource.
[这两者应该是有相关性的，对resource卡得越紧，某种程度上也可以理解为抽象程度更高？不过好像也不是这样]……
10、三个代表性的Cloud Computing产品
Amazon : EC2 （最底层的基本上就是个hardware virtual machines）
Microsoft ： Azure （介于两者之间，用.net库编写，之后会编译成CLR）
Google： AppEngine （抽象度最高）
CLR： Common Language Runtime, language-independent managed enviorenment.
AppEngine: enforcing an application structure of clean separation between a stateless computation tier and a stateful storage tier. (是说无国界的计算，但存储分国家吗？)
11、When is Utility Computing preferable to running a Private Cloud?
① when demand for a service varies with time.
（某个服务可能一个月中有几天会达到负载的峰值，但其他时候负载一般）
② when demand is unknown in advance
（如，对网站而言，当其流行时，访问量可能会激增，但当访问者流失时又会下降，这些变化是很难预知的）
③ organizations that perform batch analytics（批量分析）can use the "cost associativity" of cloud computing to finish computation faster.
（因为 使用1000台EC2机器运行1小时的费用 和 使用1台EC2机器运行1000小时 的费用是相同的，但前者却可以很快拿到计算结果）