What is Azure AD ?

Microsoft Azure Active Directory (Azure AD) is a cloud-based identity and access management solution. Its primary purpose is to provide authentication and authorization when accessing cloud-based resources. However, you can also leverage its functionality to protect on-premises applications. In both cases, you can further streamline and enhance secure access to sensitive services and data by taking advantage of Azure AD’s single sign-on (SSO), federation, and Microsoft Azure Multi-Factor Authentication capabilities. 

VHD vs VHDX

Virtual hard disks typically use the .vhd extension. Windows Server 2012 introduces a new type of virtual hard disk that uses the .vhdx extension. Virtual hard disks with the .vhdx format have the following benefits over virtual hard disks that were used in Hyper-V on Windows Server 2008 and Windows Server 2008 R2:

• Virtual hard disks with the .vhdx format can be as large as 64 terabyte (TB), whereas virtual hard disks with the .vhd format are limited to 2 TB.
  
• Virtual hard disks with the .vhdx format are less likely to become corrupt if the virtualization server suffers an unexpected power outage.
  
• The .vhdx format supports better alignment when deployed to a large sector disk.
  
• Virtual hard disks with the .vhdx format can hold larger dynamic and differencing virtual hard disks. This provides for better performance from the dynamic and differencing virtual hard disks.

You can convert a virtual hard disk with the .vhd format to the .vhdx format by using the Edit Virtual Hard Disk Wizard. You might want to do this if you have upgraded a Windows Server 2008 or Windows Server 2008 R2 virtualization server to Windows Server 2012 or Windows Server 2012 R2. You can also convert a virtual hard disk with the .vhdx format to the .vhd format. 

What is Azure ?

Azure is the public cloud services offering from Microsoft. Microsoft datacenters deliver Azure services over the Internet. Customers can subscribe to a variety of the Azure services that run in these datacenters, typically at a cost lower than they might incur if they purchased or hosted their own hardware, or built their own services and software.

Individuals, customers, and Microsoft partners can use several methods to access Azure–based services. Partners have access to programs such as Microsoft Azure platform Cloud Essentials for Partners and Cloud Accelerate. Both customers and partners can access resources through MSDN and through the Microsoft BizSpark program, each of which provides a predefined amount of resources and services to build solutions.