It's always the current working directory, I believe. It's usually the same as the executable's location, especially under Windows where most programs are started from a shortcut which automatically sets the CWD to the executable's location. When you're starting program.exe from a different folder, you're really starting different/folder/program.exe, it should then be clear the executable's absolute location is somewhat irrelevant.
You could always whip up a quick program to find out, though!