Operating System Overview

The 32-bit edition of Visual C++ can be used to develop programs for three Win32 platforms: Windows NT (on multiple processors), Windows 95, and Win32s.

Windows NT is Microsoft's high-end portable server operating system. It is a full-featured 32-bit multithreaded operating system with an integrated graphical environment and advanced server capabilities. Its development has been aimed to maximize portability, stability, and security. While its compatibility with well-behaved MS-DOS and Windows 3.1 applications is remarkably good, it falls short of being a 100 percent replacement for your old MS-DOS system; if you wish to run a sophisticated game program, you may have to reboot to the good old DOS command line. (Does DOOM work under Windows NT? Don't ask me; I haven't tried.)

Windows 3.1 is, of course, the omnipresent graphical environment sitting, used or unused, in a directory on just about every PC nowadays. While it delivers some operating system-like features, it is essentially a graphical environment sitting on top of MS-DOS instead of replacing it. Because of limitations in both DOS and the 16-bit Windows 3.1 architecture, the DOS-Windows system combination is inherently unstable, prone to crashes, and exposed to ill-behaved applications. The Win32s subsystem is yet another layer on top of Windows 3.1; it implements a subset of the Win32 system calls that enables many simpler 32-bit applications (or complex ones that were written with Win32s compatibility in mind) to run.

Microsoft's new operating system, Windows 95, offers the best of both worlds. Unlike Windows NT, Windows 95 has been written with backward compatibility as one of the main design criteria. Despite this and the fact that Windows 95 inherited a significant amount of legacy code from Windows 3.1, it has remarkably few shortcomings. Its stability is comparable to Windows NT, its performance exceeds that of both Windows NT and Windows 3.1, and its hardware resource requirements are minimal, comparable to that of Windows 3.1.

Despite the obvious differences between these platforms (the most notable is the restrictions placed on applications intended to run in the Win32s environment), they share most essential features. In particular, most simple applications are expected to be compatible with all three of these platforms with little or no modification. For this reason, I usually discuss operating system or compiler features without regard to the target operating system; if significant platform differences exist, however, I mention those.

Windows and Messages

Windows is often referred to as a message-passing operating system. At the very heart of the system is the mechanism that translates just about every event (a keypress, a mouse movement, a timer countdown) into a message; typical applications are built around a message loop that retrieves these messages and dispatches them to the appropriate message handler functions.

Messages, although sent to applications, are not addressed to them; they are, instead, addressed to what are the other fundamental components of the operating system, windows. A window is much more than merely a rectangular area of the computer's screen; it also represents an abstract entity through which the user and the application interact with each other.