Traditionally, Remote Desktop Services (previously Terminal Services) provided the ability to host multiple, simultaneous user sessions on a single server. Windows Server 2008 R2 expanding Remote Desktop Services to also enable a Virtual Desktop Infrastructure (VDI). Microsoft VDI provides the ability to run multiple client operating systems (OS) on a single server hosted on Hyper-V. This post illustrates the role that RDS role services play in Microsoft VDI architecture. Scenarios: Personal virtual desktops’re virtual machines that’re permanently assigned to users by an administrator. This configuration’s saved in Active Directory Domain Services. A personal virtual desktop’s typically used when a user needs a dedicated virtual machine (VM) with administrative privileges (for example, a user might want to install applications). A virtual desktop pool is a group of identically configured virtual machines that are temporarily assigned to users by the Microsoft VDI system. Administrators can configure a VM to be a part of a pool.
Full Article: Directory Services blog