New
#81
To backup the registry, you copy the registry hives (BCD, DEFAULT, SAM, SECURITY, SOFTWARE, SYSTEM, NTUSER.DAT, the filenames are all capital).
Most of these registry hives are located in %SystemRoot%\System32\Config\, the NTUSER.DAT hive is located in %USERPROFILE%.
There are some other registry hives, such as COMPONENTS, DRIVERS and ELAM, but some of them are only loaded when they're needed (such as COMPONENTS for Windows Update).
If you're going to backup these hives, I want to urge you to not import these hives into the new registry permanently. You can import the hives to look up the differences and make the necessary edits for the programs, but I would not recommend for anything else.