Windows 9x

Windows 9x

Operating systems continue to evolve as hardware and software technologies improve. If you look at several operating systems, you will see the evolution process from DOS to DOS with Windows 3.x, to Windows 9x. To understand these gradual improvements in operating systems, you need to understand the following terms:

Multitasking, as it applies to hardware, refers to the ability of a CPU to do more than one thing at a time. The first CPU for microcomputers with this ability was the Pentium by Intel. The older i386 and i486 CPUs could do only one thing at a time (80386 and 80486 CPUs are often abbreviated as i386 and i486 in documentation; the i stands for the chip manufacturer, Intel). Earlier operating systems did not need to support multitasking; newer operating systems now need to support some form of multitasking.

Cooperative multitasking, sometimes called task switching, is not true multitasking, in that the CPU is only doing one thing at a time. The CPU is switching back and forth between applications so that more than one application can be loaded at the same time. There is only one active application and one or more inactive applications sitting in the background waiting for the active application to relinquish control.

You’ve observed cooperative multitasking if you’ve ever had two applications open, each in its own window. You don’t need to close one application before opening another. DOS does not handle cooperative multitasking, but Windows does.

Preemptive multitasking is another type of pseudo-multitasking whereby the operating system allots CPU time to an application for a specified period, and then preempts the processing to give the CPU to another application. The end result is that the computer appears to be doing true multitasking.

Environment refers to the type of support the operating system provides to the applications software. For example, in order for applications software to offer you a window with mouse movement, buttons to click, and icons to view, a GUI environment, such as Windows, must support it. Such an application is said to need a “GUI environment” to work. Another example is the DOS environment that offers to its applications software only a “single-tasking environment.” The software does not expect another applications software package to be running concurrently with it.

There is a unique situation with Windows 3.x. It’s not really an operating system, but neither does it act like normal applications software. Windows 3.x provides an operating environment, which refers to the overall support that it provides to applications software, including cooperative multitasking and a GUI (which DOS does not offer). Windows 3.x is the “middleman” that manages this pseudo multitasking environment by passing tasks to DOS one at a time. DOS manages its single-tasking environment and relates to the hardware in single-task fashion. Windows provides the cooperative multitasking environment to the applications.

Comparing Windows 9x, Windows 3.x, And DOS

In the following figure, you see that Windows 9x is an operating system that bridges two

worlds. DOS/Windows 3.x is a 16-bit world with memory management centered on conventional, upper, and extended memory limitations.

Windows 9x still has a DOS-based core, still uses many 16-bit programs, and must manage base, upper, and extended memory in basically the same way as DOS does.

However, Windows 95 introduced 32-bit programming, dynamically loaded device drivers, memory paging, networking, and many other features available in Windows NT and Windows 2000. Windows 9x claims to be completely backward compatible with older software and hardware designed to work in a DOS and Windows 3.x environment.

Windows 9x uses cooperative multitasking when supporting 16-bit applications and preemptive multitasking when supporting 32-bit applications.

Windows NT is the break with the past. It does not claim total backward compatibility because it is a freshly designed operating system with new ways of managing software and hardware resources. Software written for DOS or Windows 3.x might not work in Windows NT because the methods and rules have changed.

While Windows 95 and Windows 98 are actual operating systems, Windows 3.x is

just a GUI, or graphical user interface, used as a user-friendly intermediate program

between DOS and the user.