BIOS won't save default boot hard drive

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notasandwich

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Jun 13, 2011
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I recently bought and installed an ASUS P8B75-V motherboard. Due to some (most likely) unrelated issues I've installed Windows 7 on two separate drives, deleting the windows installation that I am not using so that their is only one installation at a time. Anyway, I've noticed that whenever I reboot my machine I get the "bootmgr is missing" message. This is easily fixed by going into the bios and changing the boot order to have the hard drive with the windows installation boot first, but regardless of how many times I save the BIOS settings to boot from the correct hard drive it always seems to go back to having the hard drive that used to have the windows 7 installation boot first. Why is this happening and what can I do to fix it?
 
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Pinhedd

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When you deleted the partition from the other drive that contained the second copy of Windows 7 you deleted the Windows 7 partition but may have missed something else.

On older motherboards with BIOS firmware the user selects a boot device, then the firmware loads the first sector of that device into system memory and transfers execution to it. The first sector on a hard disk is called the Master Boot Record which contains a small program to target and load the first sector of a partition. The first sector of each partition is called a Volume Boot Record which contains the code to load the program on that partition (usually starting with the boot loader for an OS kernel).

With the introduction of UEFI and the GPT partitioning scheme, the whole boot process has changed to be much more user friendly. The firmware now scans all storage devices for UEFI bootable partitions before hand and enumerates them.

In addition to this, the firmware also retains the ability to target traditional MBR formatted drives the old fashioned way. Even if you leave your current drive as the first one in the boot order MBR style, it may still target a GPT partition on the other drive if the UEFI scheme is prioritized over the legacy scheme.

You can disable this in the UEFI settings under "Compatibility Support Module" by setting the storage settings to "UEFI Only". As a warning though, this may break any RAIDs created using the Intel Rapid Storage Technology OPROM.

If you want to make sure that the other drive is completely free of any Windows bootable environment, use a drive initialization software such as that included with PartedMagic or DBAN to completely wipe it.
 
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notasandwich

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