Windows NT and Windows 2000 store the ProductType, a string value, at HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\ProductOptions.

If described the data values for Windows NT in tip 1826.

When Windows 2000 was released, these codes acquired new meanings:

WinNT    Windows 2000 Professional  ServerNT Windows 2000 Server  LanmanNT Windows 2000 Server configured as a domain controller.
In addition to ProductType, the ProductSuite, a REG_MULTI_SZ data value, contains special operating system variations installed on your computer.

NOTE: Do NOT alter this value or the operating system will accuse you or tampering.

A convenient way to view this information, and other product related values, is to download and run, as the Figure shows.