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Today when I went to boot into Windows 7, I was surprised to see that the option to boot into Windows was missing in the OS X boot manager (by holding down option). In an attempt to fix this, I installed the rEFIt boot manager. The Windows partition shows there, but once i select it it starts to boot Windows, until I get the following error message:

Missing operating system

What? Why?

I am quite sure that the operating system and all it's data is still there, but I just seem unable to boot into it. What can I do to force my Macbook to boot to it? Am I able to 'rebuild' the boot manager or partition table?

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The "missing operating system" error gives me nightmares. It usually occurs when you have some major issues with your hard drive and/or boot sector. But on a Mac it seems even harder to solve. – alex Dec 18 '09 at 9:23
up vote 1 down vote accepted

It seems that the Windows 7 partition has been corrupted in some ways (happens to me with Vista when installing Snow Leopard).

Do you have access to the Windows 7 partition from OS X ? If yes, then perform a backup. Then, boot on the Windows 7 DVD to see if you can perform a system recovery.

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I had this problem when I tried (unsuccessfully) to triple-boot my system to include Ubuntu. The fix is to boot into the Windows 7 disk, and allow it to detect that there is a problem with the boot area. It should fix it then. This page might also be of assistance.

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