How does CurrentControlSet differ from ControlSet001 and ControlSet002?

Question

In the Windows registry, how does CurrentControlSet differ from ControlSet001 and ControlSet002? Which should be set when installing for all users?

We are trying to add an environment variable for all users. Is this correct?

HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Envinronment 

Answer 1

Yes, you only need to update the CurrentControlSet key...

ControlSet001 and ControlSet002 are alternating backups of CurrentControlSet, you don't need to update them.

Edit: As K noted, CurrentControlSet is an alternating symbolic link to either ControlSet001 or ControlSet002. The other key is kept as a backup for the Load Last Known Good Configuration boot option.

Edit 2: See Microsoft KB Article 100010: What are Control Sets? What is CurrentControlSet?
Original page link broken, see archive.org backup page instead.

Answer 2

CurrentControlSet is technically not a "backup" as Gordon states.
It is a symbolic link to one of the ControlSets on the computer. It always points to the ControlSet that is currently loaded.