The following requirements drove the specification of Windows NT back in 1989:
Provide a true 32-bit, preemptive, reentrant, virtual memory operating system
Run on multiple hardware architectures and platforms
Run and scale well on symmetric multiprocessing systems
Be a great distributed computing platform, both as a network client and as a server
Run most existing 16-bit MS-DOS and Microsoft Windows 3.1 applications
Meet government requirements for POSIX 1003.1 compliance
Meet government and industry requirements for operating system security
Be easily adaptable to the global market by supporting Unicode
To guide the thousands of decisions that had to be made to create a system that met these requirements, the Windows NT design team adopted the following design goals at the beginning of the project:
Extensibility. The code must be written to comfortably grow and change as market requirements change.
Portability. The system must be able to run on multiple hardware architectures and must be able to move with relative ease to new ones as market demands dictate.
Reliability and robustness. The system should protect itself from both internal malfunction and external tampering. Applications should not be able to harm the operating system or other applications.
Compatibility. Although Windows NT should extend existing technology, its user interface and APIs should be compatible with older versions of Windows and with MS-DOS. It should also interoperate well with other systems, such as UNIX, OS/2, and NetWare.
Performance. Within the constraints of the other design goals, the system should be as fast and responsive as possible on each hardware platform.
As we explore the details of the internal structure and operation of Windows, you’ll see how these original design goals and market requirements were woven successfully into the construction of the system. But before we start that exploration, let’s examine the overall design model for Windows and compare it with other modern operating systems.