|
The architecture of Windows NT, a line of operating systems produced and sold by Microsoft, is a layered design that consists of two main components, user mode and kernel mode. It is a preemptive, reentrant operating system, which has been designed to work with uniprocessor and symmetrical multi processor (SMP)-based computers. To process input/output (I/O) requests, they use packet-driven I/O, which utilizes I/O request packets (IRPs) and asynchronous I/O. Starting with Windows 2000, Microsoft began making 64-bit versions of Windows available; before this, these operating systems only existed in 32-bit versions. Programs and subsystems in user mode are limited in terms of to what system resources they have access, while the kernel mode has unrestricted access to the system memory and external devices. The Windows NT kernel is known as 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. User mode in Windows NT is made of subsystems capable of passing I/O requests to the appropriate kernel mode device drivers by using the I/O manager. The user mode layer of Windows NT is made up of the "Environment subsystems," which run applications written for many different types of operating systems, and the "Integral subsystem," which operates system specific functions on behalf of environment subsystems. Kernel mode in Windows NT has full access to the hardware and system resources of the computer. The kernel mode stops user mode services and applications from accessing critical areas of the operating system that they should not have access to. The Executive interfaces, with all the user mode subsystems, deals with I/O, object management, security and process management. The kernel sits between the Hardware Abstraction Layer and the Executive to provide ''multiprocessor synchronization'', thread and interrupt scheduling and dispatching, and trap handling and exception dispatching. The kernel is also responsible for initializing device drivers at bootup. Kernel mode drivers exist in three levels: highest level drivers, intermediate drivers and low level drivers. Windows Driver Model (WDM) exists in the intermediate layer and was mainly designed to be binary and source compatible between Windows 98 and Windows 2000. The lowest level drivers are either legacy Windows NT device drivers that control a device directly or can be a plug and play (PnP) hardware bus. ==User mode== The user mode is made up of subsystems which can pass I/O requests to the appropriate kernel mode drivers via the I/O manager (which exists in kernel mode). The user mode layer of Windows NT is made up of the ''Environment subsystems'' and the ''Integral subsystem''. The environment subsystems were designed to run applications written for many different types of operating systems. None of the environment subsystems can directly access hardware, and must request access to memory resources through the Virtual Memory Manager that runs in kernel mode. Also, applications run at a lower priority than kernel mode processes. There are three main environment subsystems: the Win32 subsystem, an OS/2 subsystem and a POSIX subsystem.〔(【引用サイトリンク】title=Appendix D - Running Nonnative Applications in Windows 2000 Professional )〕 *The Win32 environment subsystem can run 32-bit Windows applications. It contains the console as well as text window support, shutdown and hard-error handling for all other environment subsystems. It also supports Virtual DOS Machines (VDMs), which allow MS-DOS and 16-bit Windows (Win16) applications to run on Windows NT. There is a specific MS-DOS VDM that runs in its own address space and which emulates an Intel 80486 running MS-DOS 5.0. Win16 programs, however, run in a Win16 VDM. Each program, by default, runs in the same process, thus using the same address space, and the Win16 VDM gives each program its own thread on which to run. However, Windows NT does allow users to run a Win16 program in a separate Win16 VDM, which allows the program to be preemptively multitasked, as Windows NT will pre-empt the whole VDM process, which only contains one running application. The Win32 environment subsystem process (csrss.exe) also includes the window management functionality, sometimes called a "window manager". It handles input events (such as from the keyboard and mouse), then passes messages to the applications that need to receive this input. Each application is responsible for drawing or refreshing its own windows and menus, in response to these messages. *The OS/2 environment subsystem supports 16-bit character-based OS/2 applications and emulates OS/2 1.x, but not 32-bit or graphical OS/2 applications as used with OS/2 2.x or later, on x86 machines only.〔(【引用サイトリンク】title=Windows NT Workstation Resource Kit Chapter 28 - OS/2 Compatibility )〕 To run graphical OS/2 1.x programs, the Windows NT Add-On Subsystem for Presentation Manager must be installed.〔 The last version of Windows NT to have an OS/2 subsystem was Windows 2000; it was removed as of Windows XP.〔(【引用サイトリンク】title=POSIX and OS/2 are not supported in Windows XP or in Windows Server 2003 )〕 *The POSIX environment subsystem supports applications that are strictly written to either the POSIX.1 standard or the related ISO/IEC standards. This subsystem has been replaced by Interix, which is a part of Windows Services for UNIX.〔 The integral subsystem looks after operating-system specific functions on behalf of the environment subsystems. It consists of a ''security subsystem'', a ''workstation service'' and a ''server service''. The security subsystem deals with security tokens, grants or denies access to user accounts based on resource permissions, handles login requests and initiates login authentication, and determines which system resources need to be audited by Windows NT. It also looks after Active Directory. The workstation service is an API to the network redirector, which provides the computer access to the network. The server service is an API that allows the computer to provide network services. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Architecture of Windows NT」の詳細全文を読む スポンサード リンク
|