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The Windows NT kernel is a hybrid kernel; the architecture comprises a simple kernel, hardware abstraction layer (HAL), drivers, and a range of services (collectively named Executive), which all exist in kernel mode. [1] User mode in Windows NT is made of subsystems capable of passing I/O requests to the appropriate kernel mode device drivers ...
Windows NT uses a layered design architecture that consists of two main components, user mode and kernel mode. Programs and subsystems in user mode are limited in terms of what system resources they have access to, while the kernel mode has unrestricted access to the system memory and external devices. Kernel mode in Windows NT has full access ...
When called from ntdll.dll in user mode, these groups are almost exactly the same; they execute an interrupt into kernel mode and call the equivalent function in ntoskrnl.exe via the SSDT. When calling the functions directly in ntoskrnl.exe (only possible in kernel mode), the Zw variants ensure kernel mode, whereas the Nt variants do not. [1]
When called from ntdll.dll in user mode, these groups are almost exactly the same; they trap into kernel mode and call the equivalent function in ntoskrnl.exe via the SSDT. When calling the functions directly in ntoskrnl.exe (only possible in kernel mode), the Zw variants ensure kernel mode, whereas the Nt variants do not. [7]
The Client/Server Runtime Subsystem, or csrss.exe, is a component of the Windows NT family of operating systems that provides the user mode side of the Win32 subsystem.In modern versions of Windows, it is primarily involved with process and thread management, console window handling, side-by-side assembly loading and the shutdown process.
In most existing systems, switching from user mode to kernel mode has an associated high cost in performance. It has been measured, on the basic request getpid, to cost 1000–1500 cycles on most machines. Of these just around 100 are for the actual switch (70 from user to kernel space, and 40 back), the rest is "kernel overhead".
The Session Manager Subsystem is the first user-mode process started by the kernel. Once started it creates additional paging files with configuration data from HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management, [1] the environment variables located at the registry entry HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Environment, and DOS device mappings (e.g. CON ...
Enterprise Server was designed for high-demand, high-traffic networks. Windows NT 4.0 Server, Enterprise Edition includes Service Pack 3. [37] The Enterprise Edition saw the introduction of the /3GB boot flag, which changed the default virtual address space mapping from 2 GB kernel and 2 GB user space to 1 GB kernel and 3 GB userland. [38]