Windows 8 Startup Process

When you switch on a computer, the startup process loads the BIOS. When it loads the BIOS, the system
accesses the boot disk’s Master Boot Record (MBR), followed by the drive’s boot sector.

The Windows 8 startup process has seven steps:

1. The BIOS performs a Power On Self-Test (PoST). From a startup perspective, the BIOS enables the computer to access peripherals, such as hard disks, keyboards, and the computer display, prior to loading the operating system.

2. The computer uses information in the BIOS to locate an installed hard disk, which should contain an MBR. The computer calls and loads Bootmgr.exe, which then locates an active drive partition on sector 0 of the discovered hard disk.

3. Bootmgr.exe reads the BCD file from the active partition, gathers information about the machine’s installed operating systems, and then displays a boot menu, if necessary.

4. Bootmgr.exe transfers control to winload.exe, or it calls winresume.exe for a resume operation. If winload.exe selects a down-level operating system, such as Windows XP  Professional, Bootmgr.exe
transfers control to NTLDR.

5. Otherwise, winload.exe initializes memory and loads drivers that are set to begin at startup. These drivers are for fundamental hardware components, such as disk controllers and peripheral bus drivers. Winload.exe then transfers control to the kernel of the operating  system, ntoskrnl.exe.

6. The kernel initializes, and then higher-level drivers, except BOOT_START and services, are loaded. During this phase, you will see the screen switch to graphical mode as  the Windows subsystem is
initialized by the session manager (Smss.exe).

7. The operating system displays the logon splash screen, and a user logs on to the computer