NT 4
NT 4.0 WorkstationMicrosoft Windows NT Workstation 4.0 is one of the most powerful 32-bit operating systems available for business computing today. It offers the ease of use of Windows 95 along with higher performance, greater reliability, and better security.
One of the most remarkable aspects of Windows NT's architecture is that portions of the operating system--the subsystems--run in user-mode processes alongside application processes. The subsystems provide the environments in which applications run. The Win32 subsystem provides the application program interface (API) services that Win32 applications call to do useful things such as create windows and open files. Applications and subsystems enjoy a client/server relationship in which the applications are the clients and the subsystems are the servers. One of the benefits of this architecture is that you can include support for other types of applications (such as Unix applications) to Windows NT simply by adding subsystems.
Much of Windows NT's renowned stability is a direct result of the operating system's architecture. Applications can't interfere with one another because they run in separate address spaces. Operating system code and data in the subsystems is protected from applications because subsystems, too, reside in their own address spaces. The Windows NT Executive shares address space with running processes, but it's protected by the wall between kernel mode and user mode. It's impossible for an application to corrupt code or...
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