![]() Kernel-mode DLL that interfaces Ntoskrnl and drivers to the hardware. Initializes executive subsystems and boot and system-start device drivers, prepares the system for running native applications, and runs Smss.exe. If selected from the Boot Manager, starts up and provides a graphical interface for scanning memory and detecting damaged RAM. If resuming after a hibernation state, resumes from the hibernation file (Hiberfil.sys) instead of typical Windows loading. Loads Ntoskrnl.exe and its dependencies (Bootvid.dll on 32-bit systems, Hal.dll, Kdcom.dll, Ci.dll, Clfs.sys, Pshed.dll) and boot-start device drivers.ģ2-bit protected mode, 64-bit protected mode if resuming a Win64 installation If a 64-bit installation is booted, switches to 64-bit long mode before loading Winload.ģ2-bit protected mode with paging, 64-bit protected mode if booting a Win64 installation Reads the Boot Configuration Database (BCD), presents boot menu, and allows execution of preboot programs such as the Memory Test application (Memtest.exe). Understands the file system on the partition and locates Bootmgr by name, loading it into memoryġ6-bit real mode and 32-bit without paging Reads and loads the volume boot record (VBR)īoot sector (also called volume boot record) (You can learn more about Windows partitioning in Chapter 9.) Table 13-1 Bios Boot Process Components Figure 13-1 shows an example of a hard disk layout, and Table 13-1 summarizes the files involved in the BIOS boot process. Extended partitions can contain extended partitions, which can contain extended partitions, and so on, making the number of volumes an operating system can place on a disk effectively infinite. Because this apportioning scheme would limit a disk to four volumes, a special partition type, called an extended partition, further allocates up to four additional partitions within each extended partition. A hard disk can contain up to four primary partitions. Microsoft operating systems split hard disks into discrete areas known as partitions and use file systems (such as FAT and NTFS) to format each partition into a volume. Since the early days of MS-DOS, a standard has existed on x86 systems for the way physical hard disks are divided into volumes. Before we get into what this code does, let’s look at how and where Windows places the code on a disk. ![]() At some point during the execution of the Windows Setup program, the system’s primary hard disk is prepared with code that takes part in the boot process. It begins when you install Windows on your computer. The Windows boot process doesn’t begin when you power on your computer or press the reset button. To support these different firmware implementations (as well as EFI 2.0, which is known as Unified EFI, or UEFI), Windows provides a boot architecture that abstracts many of the differences away from users and developers in order to provide a consistent environment and experience regardless of the type of firmware used on the installed system. The next sections describe the portions of the boot process specific to BIOS-based systems and are followed with a section describing the EFI-specific portions of the boot process. EFI is a newer standard that does away with much of the legacy 16-bit code that BIOS systems use and allows the loading of preboot programs and drivers to support the operating system loading phase. The early phases of the boot process differ significantly on systems with a BIOS (basic input output system) versus systems with an EFI (Extensible Firmware Interface). Along the way, we’ll highlight the points at which various on-screen messages appear to help you correlate the internal process with what you see when you watch Windows boot. Then we’ll describe how the executive subsystems initialize and how the kernel launches the user-mode portion of Windows by starting the Session Manager process (Smss.exe), which starts the initial two sessions (session 0 and session 1). Device drivers are a crucial part of the boot process, so we’ll explain the way that they control the point in the boot process at which they load and initialize. In describing the Windows boot process, we’ll start with the installation of Windows and proceed through the execution of boot support files. Finally, we’ll explain what occurs on an orderly system shutdown. ![]() ![]() Then we’ll explain the kinds of things that can go wrong during the boot process and how to resolve them. Understanding the details of the boot process will help you diagnose problems that can arise during a boot. ![]()
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