Running the actual operating system in an isolated sandbox.

Not all simulators are created equal. If you are searching for a training tool, ensure it offers the following:

Set up mock networks to test DNS, DHCP, and file-sharing permissions.

Take a clean snapshot immediately after finishing the basic installation. If you accidentally corrupt the directory or infect the machine during a security test, you can revert to a pristine state in seconds. Conclusion: The Move to Modern Standards

This is the most common form of "simulation." You can run the OS inside software like Oracle VirtualBox or VMware Workstation . This allows you to test server roles, Active Directory, and IIS in a safe, sandboxed environment.