The Windows Hard Drive Disk Signature
How the latest Windows operating systems
use the Disk Signature in their boot process.
There comes a point during the computer boot sequence when control is passed to a Windows component on the boot hard drive. From Windows Vista onwards this component is called bootmgr and this is the Microsoft bootmanager that has taken the place of the previous ntldr bootmanager that was part of XP and earlier WinNT operating systems. Just like the ntldr before it this new bootmanager is capable of booting not only the WIndows install it is a part of, but also other Windows operating systems that you may have on separate partitions or on additional hard drives in the PC. Unlike the ntldr however the bootmgr uses the disk signature to locate the hard drive that it wants. When bootmgr is tasked with starting an operating system it will scan all connected hard drives looking for the disk signature of the drive that the target OS is on. If the sought after signature is not found then bootmgr cannot continue with its task and so will stall with an error message. Even if you only have one hard drive and one operating system the disk signature check is still a default part of the boot process, hence issues with the disk signature can affect not only multibooters, but any Windows machine, (for GPT styled hard drives - see side box below).
How to Lose a Disk Signature.
Moving Windows to a Different Hard Drive.
The other crucial factor when moving new Windows is the starting sector of its partition. The bootmgr program uses sector numbers to locate partitions and so if the start of a partition has moved on a drive then the number of the first sector will have changed and bootmgr will fail to find that partition and consequently winload.exe, so the familiar error message will appear. For a much fuller examination of the new Windows boot files and how they operate.... see The New Generation Boot FIles - bootmgr and BCD.
Operating systems have to be GPT aware to use such drives and the Windows OSes that can will no longer use MBR signatures to identify them but rather a unique GUID number that each drive will already have as part of the GPT partitioning scheme. These GUID numbers will be considered and even called the drive's disk signature and will be used in the boot process in the same way MBR signatures are used on traditionally partitioned drives. MBR or GPT