All the previous Microsoft Windows Server products since Windows NT have been using NT Loader (NTLDR) and boot.ini to control the boot process and to manage multi operating system environments. For a BIOS based computer that is booting from its hard drive, the BIOS reads the Master Boot Record (MBR) and transfers control to the Master Boot Record (MBR) code. Master Boot Record (MBR) then transfers control to the code that loads the Operating System. NT Loader (NTLDR) is then responsible for loading Windows. NTLDR uses the data from a text file named boot.ini kept on the root folder of the boot drive.
boot.ini text file contains an entry for each version Windows installed on that computer. If multiple versions of Windows are available, NTLDR displays the list of boot entries to allow the user to specify which one should be loaded. NTLDR then loads the Operating System which the user has selected.
Microsoft has re-engineered the entire boot process in Windows 2008 Server and a new concept of Boot Configuration Data (BCD) is introduced. The Boot Configuration Data (BCD) store contains boot configuration parameters and controls how the Windows 2008 Server Operating System is started. The Boot Configuration Data (BCD)
replaces NTLDR in its functionality and the boot configuration data which was configured in boot.ini is now stored in a binary format which can be edited by the tool BCDEdit.exe. You can also use The Startup and recovery dialog box, System Configuration utility (Msconfig.exe), and BCD WMI provider to edit the Boot Configuration Data (BCD).
For BIOS-based Operating Systems, the Boot Configuration Data BCD) is located in the \Boot\Bcd directory of the active partition. For EFI–based operating systems the Boot Configuration Data (BCD) is located on the EFI system partition.
Following new boot applications are present in Windows 2008 Server.
• Bootmgr - Controls the boot flow
• Winload.exe - The Operating System Loader
• Winresume.exe - Operating System Resume Loader after a hibernation.
Source of Information: Microsoft White Paper on Boot Configuration Data