The three most important virtual device drivers are: Virtual Machine Manager (VMM32.VXD) Responsible for memory management, event handling, interrupt handling, loading and initializing virtual device drivers, creating new virtual machines and threadscheduling. The virtual device drivers are responsible for handling physical devices (such as video and network cards), emulating virtual devices used by the virtual machines or providing various system services. The lowest level of the operating system consists of a large number of virtual device drivers (VxDs) running in 32-bit protected mode and one or more virtual DOS machines running in virtual 8086 mode. The Windows 95 architecture is an evolution of Windows for Workgroups' 386 enhanced mode. Windows 95 was designed to be maximally compatible with existing MS-DOS and 16-bit Windows programs and device drivers, while offering a more stable and better performing system. The first version of Chicago's feature specification was finished on September 30, 1992. MS-DOS 7.0 was in development at that time under the code name 'Jaguar' and could optionally run on top of a Windows 3.1-based 32-bit protected-mode kernel called 'Cougar' in order to better compete with DR-DOS. Windows 93 would ship together with MS-DOS 7.0, offering a more integrated experience to the user and making it pointless for other companies to create DOS clones.
Initially, the decision was made not to include a new user interface, as this was planned for Cairo, and only focus on making installation, configuration, and networking easier. So the development of Windows 'Chicago' was started and, as it was planned for a late 1993 release, became known as Windows 93 which was also known as Windows 4.0.
Microsoft realized they were in need of an updated version of Windows that could support 32-bit applications and preemptive multitasking, but could still run on low-end hardware (Windows NT did not). Simultaneously with Windows 3.1's release, IBM started shipping OS/2 2.0.
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