Dual boot or multi boot is a state when you have more than one operating system installed on your computer. When we use the phrase “on computer” it actually means the computer system as the whole and not separate hard drives. You can have two operating systems on separate hard drives but they will necessarily not work if connected to one computer. You need special configuration changes to be done before you can make both the operating systems usable and bootable on one single machine. Windows Vista and Windows XP operating systems use a completely different set of files used for booting. Windows XP uses the Boot.Ini file to save the operating system location and Windows Vista uses Boot Configuration Database to save the operating system settings. Since Windows XP came before Windows Vista so it know nothing about it and its Boot.Ini cannot be configured for making Windows Vista to boot. But we definitely can configure the Windows Vista’s Boot Configuration Database to know about the existence of Windows XP and make it bootable if needed.

It is not only the case between Windows XP and Windows Vista but it stands true for all the operating systems. For example if you have Windows XP installed on your computer and then you install Windows 98 on it, then Windows XP will not boot. Similarly if you have Windows Vista on your computer and then you install Windows XP on it then Windows Vista will not boot. This happens because the operating system which is installed afterwards overwrites the MBR in its own style and thus makes the previous operating system unusable. It is always recommended that if you are making a multi boot computer; install the operating systems in the increasing order of their age. For example, if you wish to install Vista, XP, and 98 on one computer then begin the installation by first installing 98, then XP and then Vista.

In this article we will tell you how to install Windows XP and Windows Vista on the same computer assuming that Windows XP was already installed. For a dual boot to happen you need to have more than one partition on a hard drive (if you have one hard drive), or you need to have two hard drives. Turn ON your Windows XP computer and then insert the installation disk for Windows Vista. When the installation begins it will ask you for installation type. Select “Custom Installation” and proceed further. On proceeding further the installation will ask you specify the installation location. Please select some other partition or hard drive than the one on which you already have XP installed. After this follow the instructions displayed by the installation as usual and let it go through. When the installation completes your system will restart and now you will see two operating systems listed in the boot menu and you can use the keyboard to select the one which you want to boot. This boot menu stays visible for maximum 30 seconds by default and if you fail to make any choice within 30 seconds then the default operating system (Windows Vista) will load automatically.