A domain controller can communicate with all domain members or workstations but there is a limitation to the Active Directory (AD) System. The limitation is that the domain controller must host a Windows-based operating system. It means that all the domain members must also use the Windows operating system.
Fortunately, this limitation can now be overcome by use of Samba. Samba is open source software that allows workstations running other operating systems like OpenVMS, IBM System 390, UNIX and Linux to interact with the domain controller. This is advantageous as because of this network administrators gets much more flexibility in setting up a computer network. It is particularly very useful in large organizations in which different departments need different operating systems.
The recommended way to upgrade a domain is to promote domain controllers that run newer versions of Windows Server and demote older domain controllers as needed. That method is preferable to upgrading the operating system of an existing domain controller. You promote a domain controller that runs a newer version of Windows Server. When you upgrade the operating system on domain controllers, the computer immediately assumes the role of domain controller after the final restart of the computer. It is not necessary to install Active Directory Domain Services (AD DS) by using the Active Directory Domain Services Installation Wizard.