Arv: the registry isn't someplace you want to go poking around in just for kicks-n-grins...unless you don't mind rebuilding your system and have nothing to loose.
Also note that the registry for one Win ver won't be utilized or have the same entries as another Win ver and there will be differnecs from a base install from one on which you've added other applications.
There are also some really good books you can get on the subject.
It can be very fascinating to learn the Windows registry but if you're asking in order to solve a sudden problem....then you may be wandering around on a mine field....
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Noah built the ark BEFORE it rained.