This chapter describes the support in the Microsoft Windows operating system
version 3.0 and later for Windows and non-Windows applications using DOS
Protected-Mode Interface (DPMI) version 1.0 functions, MS-DOS interrupts and functions in protected mode, and the NetBIOS in protected mode.
DPMI enables MS-DOS applications to access the extended memory of PC-architecture computers while maintaining system protection. It also defines a new interface, through Interrupt 31h, that protected-mode applications use for such tasks as allocating memory, modifying descriptors, and calling real-mode software.
According to the DPMI specification, the term real-mode software refers to code that runs in the low 1-megabyte address space and uses segment:offset addressing. With Windows 3.0 and later in protected mode, so-called real-mode software is actually run in virtual-8086 mode. However, because virtual-8086 mode is a close approximation of real mode, both are referred to as real mode in this chapter.
For more information about the DPMI specification, contact Intel Corporation product support, or submit a service request through Microsoft OnLine.