Editing Windows 9x (section)

===Virtual Machine Manager===
The Virtual Machine Manager (VMM) is the [[32-bit]] [[protected mode]] kernel at the core of Windows 9x. Its primary responsibility is to create, run, monitor and terminate [[virtual machine]]s.

The VMM provides services that manage memory, processes, interrupts and protection faults. The VMM works with virtual devices (loadable kernel modules, which consist mostly of 32-bit ring 0 or kernel mode code, but may include other types of code, such as a 16-bit real mode initialisation segment) to allow those virtual devices to intercept interrupts and faults to control the access that an application has to hardware devices and installed software. Both the VMM and virtual device drivers run in a single, 32-bit, flat model address space at privilege level 0 (also called ring 0). The VMM provides multi-threaded, [[preemptive multitasking]]. It runs multiple applications simultaneously by sharing CPU ([[central processing unit]]) time between the threads in which the applications and virtual machines run.

The VMM is also responsible for creating MS-DOS environments for system processes and Windows applications that still need to run in MS-DOS mode. It is the replacement for vmm.386 in Windows 3.x, and the file vmm32.vxd is a compressed archive containing most of the core VxD, including VMM.vxd itself and ifsmgr.vxd (which facilitates file system access without the need to call the real mode file system code of the DOS kernel).