Dual-boot with Windows. Part II

In the previous post we saw the different partitions we can create in an environment. These partitions are OS dependant due to the nature of the file system, however most OS will recognize the most popular filesystems. A partition will hold the load manager (this is the small program that will let us select an OS at the setup screen) and each OS installed will contain a loader that will be read by the load manager to boot the OS. For some reason, Windows calls Boot partition to the partition containing the OS with its loader, while it calls System Partition to the partition containing the load manager being pointed by the MBR/PBR of one of our storage devices.

2. Installing Windows 7: Choosing a partition

So we have chosen the SSD disk to keep our Windows 7 because it will increase dramatically the performance. We had a previous SO in the SATA disk (Windows XP, Vista, a FreeDOS, Ubuntu, …) that we want to keep but without occupying to much space in the SATA. When we are asked to select a disk to install W7 we can access to disk manager and shrink the space occupied by other OSs

We are done here! But when we reboot of PC, we have three possible scenarios: Two of them are positive while the other will give us more work, depending on the previous preinstalled OSs in the SATA, if any.

- Pre-installed Windows: In this case, the Windows 7 installer will recognize the preinstalled OS. It will add an entry for itself in the boot manager (this entry is a boot loader, Windows calls it BCD) and will leave intact the previous entry of a Windows OS. Moreover, the System partition won't change and it will be the one hosting the Windows boot manager. Since Vista, Windows uses bootmgr as the boot manager addressed by the active partition VBR.

When you reboot, the BIOS will see the previous entry in the MBR/PBR and will jump to the partition that holds the old boot manager. It will select this boot manager from the System partition (the one from the pre-installed version!) that, back to the MBR, will display the two available OSs. We can select one of them and that will be the OS to be booted. We are going to have a multi-boot with two Windows systems.

- Pre-installed FreeDOS: The Windows 7 installer will recognize it as well and won't remove the entry from the MBR. The System partition will be still the FreeDOS partition in fact, so it will contain the manager. However as opposed to the previous case, the Windows 7 will be the only Boot partition. When we restart the computer, we'll move from the BIOS to the MBR, and from the MBR to the FreeDOS manager. Which will be in fact pointing to the Windows 7 loader! When we restart we will boot directly into Windows 7 through a too-many-steps process. This is far from being a fine tuning. This is unavoidable if we had a FreeDOS in the SATA, so we'll give steps to create an optimal environment for this case.

We don't need the manager in the SATA, but, as we didn't have any OS installed in the SSD, even if it goes first in the BIOS boot order, it will be ignored and will pass through the next option. This may seem strange, but that's exactly what happened to me! When installing Windows, it will look for system partitions (partitions containing already a manager) in other HDD to store its manager AND if it wasn't Windows, it will delete it from the boot chain to place its manager. Yuck!

As said above, we'll see how to modify ot boot chain. No worries. This is a suboptimal case where the boot chain will pass through some HDD to start Windows, but we'll see how to modify the boot chain to fix it to the optimal state. We are talking of a delay of less than half a second to boot Windows 7, but we can avoid it.

- Pre-installed Linux: Worst case. Chances are Windows installer won't have mercy on the MBR/PBR entries. It will wipe out previous entries on the MBR/PBR and will assign to itself the boot and system partitions. The good point? Well, if we were lucky as we wanted to install Windows 7 on the SSD disk, maybe it won't wipe the entries from the SATA, plus the Windows 7 boot loader will be in the system partition (that is, the boot partition and system partition will be the Windows 7 installation partition and we won't have to copy the bootloaders from one partitions to others). Depending on the disks we gave priority in the BIOS menu, we'll boot directly in Windows 7 for the SSD or, if the entries in the MBR/PBR SATA disk weren't removed, we'll boot into out pre-installed Linux. Again, I can't guarantee what a Windows installer will do on non-recognized MBR entries that could be on a different disks than the one to be installed. If you wanted to keep a previous version of a Linux system, back-up before playing the roulette (if for some reason you want to end up with a Windows7 - Previous Linux - Kali Linux environment).