DPMI Specification Available from Intel

The information in this article applies to:

• Microsoft Windows Software Development Kit (SDK) for Windows versions 3.0 and 3.1

SUMMARY

The MS-DOS protected mode interface (DPMI) specification is available free of charge by calling Intel Corporation at (800) 548-4725. International customers can obtain the DPMI Specification by contacting the Intel sales office that serves their country.

MORE INFORMATION

The DPMI specification was defined to allow an MS-DOS program to access the extended memory provided by a PC architecture computer while maintaining system protection. DPMI defines a specific subset of MS-DOS and BIOS calls that can be made by protected mode MS-DOS programs. It also defines a new interface through software Interrupt 31h, which protected mode programs can use to allocate memory, modify selectors, call real mode software, and so forth.

DPMI is commonly used to communicate with a terminate-and-stay- resident (TSR) program or an MS-DOS device driver from a protected mode application. If the protected mode application passes a buffer of data to a TSR or device driver, the application must allocate the buffer from memory addressed below 1 megabyte to make the data accessible to the real mode software. The application must also translate the buffer's address from a selector address to a segment address. If the real mode software calls back to a function in the protected mode application, the application must allocate a real mode callback address. DPMI provides services to perform each of these tasks.

The Microsoft Windows standard mode MS-DOS extender and Windows enhanced mode provide translation services for most of the commonly used interrupts. This allows a driver or an application to call MS-DOS, the BIOS, and other common services without using the DPMI. However, when an application communicates with a network, a TSR, or any real mode software for which Windows does not provide automatic translation, it must use DPMI services.

DPMI services should be used only in a Windows device driver or a dynamic-link library (DLL). An application should manipulate selectors using the kernel selector functions, documented in the Microsoft Windows Software Development Kit (SDK). Calling DPMI services from an application may not be supported by future versions of Windows. However, calling these services from a device driver or a DLL will be supported.