The Windows dual and multiboot method of operation.
The limitations of the Windows method and some alternatives.
How third-party bootmanagers operate.
|The Boot Sequence Programs|
|In these graphics the MBR is shown as a separate section at the very start of the hard drive. It is indeed separate and not connected in any way to the following partitions. Convention is to reserve a small section of the drive specifically for the MBR to reside on. I’ve shown the PBR as a separate section but it is actually a part of the partition it is in. Windows reserves the first 16 sectors of its partition to be used exclusively for the partition boot record.|
|Given free reign at install time Windows 7 may create a separate small partition just for the BCD and bootmgr files. See – Installing Win7. This is not essential for the operation of Win7 and Microsoft have said it was only introduced now so we can become familiar with the concept ahead of them making it standard practice for Windows on EFI firmware machines. |
|In old WinNT the ntldr consults the boot.ini file to find out which hard drive and partition it needs to look on for the Windows/System32 folder it has to target. The ntldr then uses the BIOS to locate the hard drive and the Partition Table to locate the partition. In Vista and Win7 the bootmgr consults the BCD file to find out which hard drive and partition it should go to, but it does not use the BIOS or the partition table to locate the drive or partition. See Vista's Boot Files|
|To make all your OSes independent and with their own boot programs on their own partition then you do of course have to install Windows in the correct manner. See "How to Install Vista and Avoid Changes to Other Operating Systems" on this page. (Similar rules apply for most WinNT OSes).|
The next best option is a bootmanager that you keep on its own small dedicated partition, often at the start of the boot hard drive, but some will use a logical partition. Even though this may sound similar to the way ntldr and bootmgr operate it does not usually require the partition to become a system partition, so each Windows install can still be independent with its own ntldr or bootmgr and loaded by its own PBR. The bootmanager partition will always be the one started by the IPL. Be aware however that most bootmanagers of this type still replace the Microsoft IPL in the MBR so that it will always target the bootmanager partition at computer startup. The Active status of partitions will be ignored by the new IPL and will instead be controlled and changed by the bootmanager itself when you make your booting choice. Many of the issues relevant to pure IPL bootmanagers can also therefore apply to dedicated partition bootmanagers.
Most dedicated partition bootmanagers can also be installed inside a current OS. They will change the PBR of that OS so that it will load the bootmanager instead of the operating system's own boot files, they also of course change the IPL in the same way as a dedicated partition bootmanager. When you select a boot option they will either start the boot files of the OS they are in, or the PBRs of the other OSes on the computer. Again there is usually no system partition and each Windows install can be independent.