下面的链接很好地解释了SaaS, PaaS和Iaas。 http://opensourceforgeeks.blogspot.in/2015/01/difference-between-saas-paas-and-iaas.html

简单来说:

IaaS，在这里，供应商向用户提供基础设施，用户获得硬件/虚拟化基础设施，存储和网络基础设施。

PaaS，在这里，供应商为用户提供平台，用户可以获得他们工作所需的所有东西，如操作系统、数据库、执行环境以及IaaS提供的环境。 所以pass是平台+ IaaS。

SaaS似乎是一个相当广泛的领域，供应商提供从基础设施到平台到软件的几乎所有东西。 所以SaaS是Iaas+PaaS加上不同的软件，如ms office，虚拟盒子等。

IaaS、PaaS和SaaS是云计算服务模式。

IaaS (Infrastructure as a Service), as the name suggests, provides you the computing infrastructure, physical or (quite often) virtual machines and other resources like virtual-machine disk image library, block and file-based storage, firewalls, load balancers, IP addresses, virtual local area networks etc. Examples: Amazon EC2, Windows Azure, Rackspace, Google Compute Engine. PaaS (Platform as a Service), as the name suggests, provides you computing platforms which typically includes operating system, programming language execution environment, database, web server etc. Examples: AWS Elastic Beanstalk, Windows Azure, Heroku, Force.com, Google App Engine, Apache Stratos. While in SaaS (Software as a Service) model you are provided with access to application software often referred to as "on-demand software". You don't have to worry about the installation, setup and running of the application. Service provider will do that for you. You just have to pay and use it through some client. Examples: Google Apps, Microsoft Office 365.

关于你的问题还有几点:

AWS(亚马逊网络服务)是一个完整的套件，包含了一大堆有用的网络服务。目前最流行的是EC2和S3，属于IaaS服务模式。 虽然Hadoop是基于谷歌之前的工作(GFS和MapReduce)，但它不是来自谷歌。它是一个Apache项目。你可以在这里找到更多。它只是一个分布式计算平台，不属于任何这些服务模型，恕我直言。 微软的Windows Azure也是IaaS的一个例子。

就这些服务的受欢迎程度而言，它们都很受欢迎。关键在于哪一种更符合你的要求。例如，如果您想要在一个Hadoop集群上运行MapReduce作业，您会发现EC2非常适合，即IaaS。另一方面，如果你有一些用某种语言编写的应用程序，你想在云上部署它，你会选择像Heroku这样的应用程序，它是PaaS的一个例子。

IaaS PaaS和SaaS的区别

在下面的表格中，我们将解释上下文的差异

  pizza as a service 

SaaS: Software as a Service Cloud application services or “Software as a Service” (SaaS) are probably the most popular form of cloud computing and are easy to use. SaaS uses the Web to deliver applications that are managed by a third-party vendor and whose interface is accessed on the clients’ side. Most SaaS applications can be run directly from a Web browser, without any downloads or installations required. SaaS eliminates the need to install and run applications on individual computers. With SaaS, it’s easy for enterprises to streamline their maintenance and support, because everything can be managed by vendors: applications, runtime, data, middleware, O/S, virtualization, servers, storage, and networking. Gmail is one famous example of an SaaS mail provider.

PaaS: Platform as a Service The most complex of the three, cloud platform services or “Platform as a Service” (PaaS) deliver computational resources through a platform. What developers gain with PaaS is a framework they can build upon to develop or customize applications. PaaS makes the development, testing, and deployment of applications quick, simple, and cost-effective, eliminating the need to buy the underlying layers of hardware and software. One comparison between SaaS vs. PaaS has to do with what aspects must be managed by users, rather than providers: With PaaS, vendors still manage runtime, middleware, O/S, virtualization, servers, storage, and networking, but users manage applications and data.

IaaS: Infrastructure as a Service Cloud infrastructure services, known as “Infrastructure as a Service” (IaaS), deliver computer infrastructure (such as a platform virtualization environment), storage, and networking. Instead of having to purchase software, servers, or network equipment, users can buy these as a fully outsourced service that is usually billed according to the amount of resources consumed. Basically, in exchange for a rental fee, a third party allows you to install a virtual server on their IT infrastructure. Compared to SaaS and PaaS, IaaS users are responsible for managing more: applications, data, runtime, middleware, and O/S. Vendors still manage virtualization, servers, hard drives, storage, and networking. What users gain with IaaS is infrastructure on top of which they can install any required platforms. Users are responsible for updating these if new versions are released.

如果你是一个简单的客户，想要使用某个软件，但手头什么也没有，那么你就使用SaaS。

当你有一个自己开发的软件，但你想在一个公共平台上部署和运行，那么你就使用PaaS。

当你已经准备好了软件和平台，但还想让硬件运行时，你就可以使用IaaS。

IaaS(基础设施即服务)

IaaS提供基础设施，如虚拟机和其他资源，如虚拟机磁盘映像库、基于块和文件的存储、防火墙、负载平衡器、IP地址、虚拟局域网等。基础设施即服务(IaaS)是云计算模型的基础层。

常见的例子:DigitalOcean、Linode、Rackspace、Amazon Web Services (AWS)、Cisco Metapod、Microsoft Azure、谷歌Compute Engine (GCE)是Iaas的一些流行例子。

平台即服务(PaaS)

PaaS或平台即服务模型为您提供计算平台，通常包括操作系统、编程语言执行环境、数据库和web服务器。从技术上讲，它是在IaaS之上的一个层，是继基础设施之后你需要的第二个东西，是一个平台。

常见的例子:AWS Elastic Beanstalk, Windows Azure, Heroku, Force.com，谷歌应用程序引擎，Apache Stratos。

软件即服务(SaaS)

在SaaS中，您可以访问安装在服务器上的应用程序服务。你不必担心软件的安装、维护或编码。您只需使用浏览器即可访问和操作该软件。你不需要下载或安装任何类型的安装或操作系统，软件只是供你访问和操作。软件维护或设置或帮助将由SaaS提供商公司提供，您只需支付使用费用。

常见的例子:谷歌应用程序，微软office365，谷歌文档，Gmail, WHMCS计费软件

IaaS, PaaS和SaaS之间的基本区别