The DOS Emulation component provides an emulation of the DOS operating system environment, including DOS features and system services, for applications running in virtual DOS machines. DOS Emulation uses the parameters specified in CONFIG.SYS and virtual device drivers to create an application-compatible DOS environment within the VDM address space.
During execution, DOS Emulation receives requests from DOS applications. Depending upon the type of request, it either processes the request itself or causes a general protection exception which results in the request being routed by the operating system kernel to the 8086 Emulation component, which processes the request at a higher privilege level.
DOS Emulation also allows DOS applications to hook interrupts, in order to modify the default behavior in response to particular events. This is achieved by providing a virtual interrupt vector table within the V86 mode address space, and routing interrupts through this table.
At VDM termination time, DOS Emulation is responsible for closing all files opened by the VDM, and cleaning up the environment to ensure that no devices are still held or memory objects allocated after termination.
DOS Emulation also provides support for applications which access the standard devices CON, AUX, and PRN. These devices are emulated within DOS Emulation itself, which processes the interrupts for these devices and returns the results to the DOS application.