Windows will automatically partition a hard disk during the installation process if an unpartitioned hard disk is selected as the target drive for the operating system. The partition structure and location of the boot files will depend on the version of Windows that is being installed. To illustrate this, 32-bit versions of Windows Vista (SP1), Windows 7 (SP1) and Windows 8.1 were installed on a virtual machine with one unpartitioned disk. The following screenshots were captured from the respective operating system after the installation was complete -
Windows Vista (SP1) - one partition was created spanning the whole disk. This partition was marked as active and contained the operating system and boot files. WinRE (the Windows Recovery Environment) was not installed -
Windows 7 (SP1) - two partitions were created. The first partition was 100 MB in size and was marked as active - containing the boot files (BOOTMGR and the BCD Store). The second partition spanned the remainder of the disk and contained the operating system files. WinRE was installed on the second partition along with the OS -
Windows 8.1 - two partitions were created. The first partition was 350 MB in size and was marked as active - containing the boot files (BOOTMGR and the BCD Store). The second partition spanned the remainder of the disk and contained the operating system files. WinRE was installed on the first partition along with the boot files -
BIOS Boot Process
The following is a simplified explanation of the Windows NT 6.* boot process on systems with BIOS firmware -
Power On Self Test is completed and hardware components are initialised.
The boot device is identified based on settings in the BIOS.
In the case of a hard disk drive, the Master Boot Record (MBR) on the boot device is loaded.
The partition table in the MBR is read and the active (bootable) partition is identified.
The active partitions starting sector is loaded (the partition table contains information about the offset (from the start of the disk) of the partitions first sector).
Executable code in the partition boot record loads the Windows Boot Manager (BOOTMGR).
BOOTMGR loads the BCD store, which contains the information required to chainload the Operating System boot loader - e.g. winload.exe.
Locating the BCD Store
The first section in this page describes the default partition structure created during the Windows installation process when Windows is installed to an unpartitioned disk. It is also possible to install Windows to a prepared disk with an existing partition structure.
During the installation of Windows the BCD store will be created on the active primary partition of disk zero.
If Windows is installed on a hard disk that does not contain any existing partitions then the location of the BCD store may not be the same as the operating system partition - this depends on the version of Windows being installed. The boot files (BCD store and BOOTMGR) will however be located on the partition that is marked as active.
If an active primary partition already exists when Windows is installed then the boot files will be installed on it irrespective of the partition chosen for the operating system, although the operating system can be installed on the active partition alongside the boot files.
Assuming the operating system is installed on a separate partition to the boot files then the active partition will not be visible in Windows Explorer as no mount point is assigned - the BCD store will therefore not be visible.
Unless a third party boot loader is installed, on systems with BIOS firmware the boot files will always be installed on the active partition of disk zero. The BCD store will be located in the boot subfolder - e.g. C:\boot\BCD.
In multiboot setups using third party boot loaders/managers the location of the BCD store can be managed by taking some precautions. Temporarily setting the partition on which Windows is to be installed as active before beginning the installation will ensure that the operating system and boot files will all be placed on the same partition. As an added bonus this also makes cloning the operating system easier as it is self-contained.
Creating partitions and the possible reasons for not using Windows Vista/2008/7/8 (and Windows Vista/2008/7/8 based WinPE) to do so is not covered in any detail here. It should be noted that Windows Vista introduced a new partitioning system that can cause incompatibility problems with previous versions of windows, other operating systems, and various third party tools. These problems are well documented here.