Windows Startup and Shutdown Processes

Windows Startup - the Processes

Windows 7 The processes Windows goes through during Start Up and Shut Down can help you determine where your PC hangs or produces a blue screen. For example the if the POST cannot detect necessary hardware or determine the boot device it will halt and not let Windows Start Up.

By knowing were a problem lies its easier to get help. At QBS PC Help we have several articles that can help track down start up and shutdown problems such as:

Beep Codes

Problems with the Power On Self Test (POST)

PC restarts many times and then boots up

PC System Fails CPU Test

Here's a list of process that occur during Windows Start Up:

1. After pressing the power button, the PC's firmware initiates a Power-On Self Test (POST) and loads firmware settings.

The POST is a set of routines including a memory check, system bus check and other low-level stuff so that the CPU can initialize the computer properly. The POST process ends when a valid system disk is detected.

All modern BIOS's allow the boot device to be set manually, so you can boot from a CD/DVD-ROM, hard disk etc.

2. Firmware reads the master boot record (MBR), and then starts Bootmgr.exe. Bootmgr.exe finds and starts the Windows loader (Winload.exe) on the Windows boot partition.

3. Essential drivers required to start the Windows kernel are loaded and the kernel starts to run, loading into memory the system registry hive and additional drivers that are marked as BOOT_START.

4. The kernel passes control to the session manager process (Smss.exe) which initializes the system session, and loads and starts the devices and drivers that are not marked BOOT_START.

5. Winlogon.exe starts, the user logon screen appears, the service control manager starts services, and any Group Policy scripts are run. When the user logs in, Windows creates a session for that user.

6. Explorer.exe starts, the system creates the desktop window manager (DWM) process, which initializes the desktop and displays it.

Windows Shutdown - the processes

Windows shutdown can produce its own set of problems especially if you are running buggy software.

The more modern your copy of Windows, better the Shut Down procedure will tend to be.

Here's what happens step by step.

1. A Windows shutdown starts when you click "shut down" from the Windows Start menu, or by pressing the power button. Shutdown can also be initiated if an application initiates Shutdown by calling an API such as ExitWindowsEx() or InitiateShutdown().

2. Windows broadcasts messages to running applications, giving them a chance to save data and settings. Applications can also request a little extra time to finish what they're doing.

3. Windows closes the user sessions for each logged on user.

4. Windows sends messages to services notifying them that a shutdown has begun, and subsequently shuts them down.

It shuts down ordered services that have a dependency serially, and the rest in parallel. If a service doesn't respond, it is shut down forcefully.

5. Windows broadcasts messages to devices, signalling them to shut down.

6. Windows closes the system session (also known as "session 0").

7. Windows flushes any pending data to the system drive to ensure it is saved completely.

P.S If you want to go deeper into this subject check out Windows On/Off Transition Performance Analysis at: http://msdn.microsoft.com/en-us/windows/

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