Windows NT Operating System Design and Basics

Two primary forces shaped the design of the Windows NT operating system: market requirements and prudent, vigorous design.

Microsoft customers around the world provided the market requirements. Customers wanted the following features.

• Portability across families of processors, such as the Intel x86 line
• Portability across different processor architectures, such as complex instruction set computing (CISC), such as the Intel x86 processors, and reduced instruction set computing (RISC), such as MIPS, DEC, and PowerPC
• Transparent support for single-processor and multiprocessor computers
• Support for distributed computing
• Built-in networking
• Industry standards compliance, such as POSIX
• Certifiable security, such as C2, Functional C2, and E3

Leading-edge thinkers in operating system theory and design developed the design goals, complementing the market requirements. The following features have been built into the Windows NT design.

• Extensibility, or modularity of Windows NT. The modular design allows Microsoft to add new modules to all levels of the operating system without compromising its existing stability.
• Portability, or the ability of Windows NT to run on both CISC and RISC processors.
• Scalability, or the ability to take full advantage of symmetric multiprocessing hardware.
• Reliability and robustness, which means that the architecture protects the operating system and its applications from damage. Applications run in their own processes and cannot read or write outside of their own address space. The operating system, in the kernel, is isolated from applications, which interact with the kernel using only well-defined user-mode application programming interfaces (APIs).
• Performance, or speed of activity. By running its high-performance subsystems in kernel mode where they interact with the hardware and with each other without thread and process transitions, Windows NT 4.0 improves performance, particularly for graphics-intensive applications, such as Microsoft PowerPoint®, by as much as 20 percent.
• Compatibility, which means that Windows NT 4.0 continues to support MS-DOS, OS/2, Windows 3.x, and POSIX applications, as well as the FAT file system and a wide variety of devices and networks.

Windows NT continues to blend together real-world experience in operating systems with some of the best ideas from the computing industry and academia on operating system theory.