If under various circumstances you had to install a second Windows OS on the same system, you should have already met the dual boot option. For those who do not know, the dual boot option appears when two or more Windows systems reside on the same computer at the same time. It will pop up before booting the system permitting the user to select which OS will boot.
This option is very useful for those who own computers with older mainboards that do not provide a quick boot selection option. Newer motherboards have this option by default and whenever two or more operating systems are available, you can simply press an F key which will determine a Bios window to emerge offering you the possibility to select the desired drive to boot.
I must confess that I am a fan of the quick boot option provided by these motherboards. In case I want to format the second HDD that stores the second Window, I can do it without needing to edit the dual boot option. Just removing the second OS won't determine the dual boot option to disappear.
It will be still shown before booting although there is just one OS available. Very unpleasant I can say.
My advice, in case you want to use only the quick boot option (not the dual boot), is that when you install the second OS, make sure you remove the IDE/SATA cable for the HDD that holds the primary Windows. Because of this, the installation won't detect that you already have a primary OS installed and won't enable the dual boot option. Otherwise, the cables plugged into the primary HDD will automatically enable it.
Boot.ini, the house of the dual boot option: Boot.ini is a system file found in the system root. Because it has a major importance for the booting process, Windows developers gave it hidden, system and read-only attributes. Don't worry though, you can easily view it and even change the attributes by yourself. Just go to My Computer/Windows Explorer > Folder Options > View and check “Show hidden files and folders