Infrastructure as a Service (IaaS) The IaaS layer offers storage and compute resources that developers and IT organizations can use to deliver business solutions. Examples: Rackspace.com

Platform as a Service (PaaS) The PaaS layer offers black-box services with which developers can build applications on top of the compute infrastructure. This might include developer tools that are offered as a service to build services, or data access and database services, or billing services. Examples: Amazon EC2, MS Azure

Software as a Service (SaaS) In the SaaS layer, the service provider hosts the software so you don’t need to install it, manage it, or buy hardware for it. All you have to do is connect and use it. Examples: Gmail, Office 360, Salesforce.com

Public clouds are virtualized data centers outside of your company’s firewall. Generally, a service provider makes resources available to companies, on demand, over the public Internet.

Private clouds are virtualized cloud data centers inside your company’s firewall. It may also be a private space dedicated to your company within a cloud provider’s data center.

Hybrid clouds combine aspects of both public and private clouds.

Elasticity and scalability The cloud is elastic, meaning that resource allocation can get bigger or smaller depending on demand. Elasticity enables scalability, which means that the cloud can scale upward for peak demand and downward for lighter demand. Scalability also means that an application can scale when adding users and when application requirements change.

Self-service provisioning Cloud customers can provision cloud services without going through a lengthy process. You request an amount of computing, storage, software, process, or more from the service provider. After you use these resources, they can be automatically deprovisioned.

Standardized interfaces Cloud services should have standardized APIs, which provide instructions on how two application or data sources can communicate with each other. A standardized interface lets the customer more easily link cloud services together.

Billing and service usage metering You can be billed for resources as you use them. This pay-as-you-go model means usage is metered and you pay only for what you consume.

Cloud security The same security principles that apply to on-site computing apply to cloud computing security.

Identity management Managing personal identity information so that access to computer resources, applications, data, and services is controlled properly.

Detection and forensics Separating legitimate from illegitimate activity.

Encryption Coding to protect your information assets.

Cloud manageability You need a consistent view across both on-premises and cloud-based environments. This includes managing the assets provisioning as well as the quality of service (QOS) you’re receiving from your service provider.

Cloud standards A standard is an agreed-upon approach for doing something. Cloud standards ensure interoperability, so you can take tools, applications, virtual images, and more, and use them in another cloud environment without having to do any rework. Portability lets you take one application or instance running on one vendor’s implementation and deploy it on another vendor’s implementation.

Cloud governance and compliance Governance defines who’s responsible for what and the policies and procedures that your people or groups need to follow. Cloud governance requires governing your own infrastructure as well as infrastructure that you don’t totally control. Cloud governance has two key components: understanding compliance and risk and business performance goals.

Data in the cloud Managing data in the cloud requires data security and privacy, including controls for moving data from point A to point B. It also includes managing data storage and the resources for large-scale data processing.