The Windows Boot Manager allows you to select between operating systems during computer startup. If the Boot Manager boots the operating system installed on the "C" drive automatically without giving you the option to select the operating system installed on the "D" drive, you must manually add that operating system into the Windows Boot Manager by running a number of commands through the Command Prompt console.
Step
Run the Command Prompt console as an administrator. To do so, click "Start" and type "CMD" (without quotes) into the search box. Right-click the option labeled "Command Prompt" and select "Run as Administrator."
Step
Type "cd c:/" (without quotes) into the Command Prompt and press "Enter" to go to root of the "C" drive.
Step
Type "bcdedit /copy {current} /d "Windows Vista"" (without quotes) if the operating system you want to add is Windows Vista. Type "bcdedit /copy {current} /d "Windows 7"" (without quotes) if the operating you want to add is Windows 7. Press "Enter" to generate a boot loader. Note down the boot loader identifier (the numbers and letters that come up within the curly brackets) after pressing the "Enter" key.
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Step
Type "bcdedit /set { } device partition=D:" (without quotes) while inserting the identifier that you noted down in the above step into the curly brackets. Press "Enter" to continue.
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Type "bcdedit /set { } osdevice partition=D:" (without quotes) while inserting the identifier that you noted down in Step 3 into the curly brackets. Press "Enter" to add the operating system to the Windows Boot Manager.
Step
Restart your computer, and the Windows Boot Manager will display the newly added operating system during computer startup.
