How Can I Find Out What OS Was Originally Installed on My Windows Server?

You can check the registry to find out if your servers were upgraded. Look for the path `ComputerHKEY_LOCAL_MACHINESYSTEMSetupUpgrade`. If that key is there, it means an upgrade occurred. You can find the previous OS version in `DownlevelBuildNumber`. Also, within `ComputerHKEY_LOCAL_MACHINESYSTEMSetup`, you might see a sub-key named `Source OS (Updated on xxx)` for detailed info on what was installed before the upgrade.

You could also explore user profiles and application folders. When performing in-place upgrades, a lot of the original structure remains intact. Checking folder creation dates in the `Program Files` directory might give you a clue about the original install.

Another place to look is the `setupact.log` file located in `C:WindowsPanther`. This log usually contains information on how the OS was initially built, especially if it was set up through automated deployment tools. Just a heads-up, those logs can get really large, so use something like Notepad++ to open them; otherwise, it'll be a slow process with the regular Notepad.

Try using the command `systeminfo | find "Original"` in Command Prompt. It can tell you about the installation date, but I've noticed it sometimes doesn't work with every version of 2019—running a plain `systeminfo` might be necessary to get the info you need.

If you have the original quotes or specifications, like for a DELL system, entering the service tag on their support site can reveal which OS came pre-installed. That's a quick way to get the details.