The Interrupt 2Fh services are a set of functions that MS-DOS drivers and TSRs call to direct Windows to carry out specific actions. The notifications are a set of functions that Windows calls to notify drivers and programs of Windows-related events. Although these functions were initially designed for use by MS-DOS drivers and TSRs, some Windows device drivers, such as display drivers and grabbers, also use them to manage the multitasking features of Windows.
A driver can call the service functions using the MS-DOS multiplex interrupt, Interrupt 2Fh. The driver sets one or more registers to specified values, sets the AX register to the desired function number, and issues the interrupt using the int instruction.
A driver can receive notifications by installing its own interrupt-handling routine in the Interrupt 2Fh interrupt chain. Once the interrupt handler is installed, the driver checks the AX register on each interrupt for function numbers that match the notifications. When the driver matches a notification, it can carry out any related actions.