windows 7 boot process

Windows 7 Boot Process
Mark E. Donaldson
1. The MBR at 0000h:7C00h finds and loads the Volume Boot Sector and the NT Boot
Sector (8 KB in size). The NT Boot Sector has the ability to read FAT32 and NTFS.
2. The NT Boot Sector finds and loads BOOTMGR.EXE from the system32 or system32/boot directory at 2000h:0000h. BOOTMGR.EXE has a 16 bit header prepended to itself. This 16 bit header checks the checksum of embedded PE.EXE and maps it at
0x400000. Execution of BOOTMGR.EXE starts in 32 bits in the BmMain function.
3. BOOTMGR.EXE checks for hibernation state. If it's found, it loads WINRESUME.EXE.
4. BOOTMGR.EXE mounts and extracts basic boot information from BCD (Boot
Configuration Data). After user selects a boot entry, it is launched using
BmLaunchBootEntry with added switches. In 64-bit systems, the CPU switches to 64-bit mode just before jumping to WINLOAD.EXE.
5. BOOTMGR.EXE loads and passes control to WINLOAD.EXE.
6. WINLOAD.EXE then loads NTOSKRNL.EXE, HAL.DLL, dependencies, boot drivers, and the SYSTEM registry hive. WINLOAD.EXE then creates a PsLoadedModuleList and
LOADER_PARAMETER_BLOCK structure which contains a memory map and options list. 7. WINLOAD.EXE then loads and executes NTOSKRNL.EXE and transfers control to the kernel using OslArchTransferToKernel. NTOSKRNL.EXE uses two phases to initialize the system.
8. NTOSKRNL.EXE phase 0 initializes the kernel itself. It calls HalInitializeBios, initializes the display driver, start the debugger, and calls KilInitializeKernel. NTOSKRNL.EXE phase 1 initializes the system. It calls Phase1InitializationDiscard, HalInitSystem,
ObInitSystem, sets the time bias for ASLR, calls PsInitialSystemProcess, and then calls StartFirstUserProcess SMSS.EXE.
9. NTOSKRNL.EXE, after stopping the debugger, then passes control to the Session
Manager SMSS.EXE.
10. SMSS.EXE loads the rest of the registry, configures the environment to run the Win32 subsystem (WIN32K.SYS) and its various processes.
11. SMSS.EXE loads the WINLOGON.EXE process to create the user session, and then starts the services and the rest of the non-essential device drivers and the security subsystem LSASS.EXE.

Revised January 10, 2010

Page 1 of 2

Windows 7 Boot Process
Mark E. Donaldson

Revised January 10, 2010

Page 2 of 2