Many popular DOS applications use memory extenders such as EMS and/or XMS to gain access to memory above the 1MB real mode addressing limit on the 80286, 80386, or 80486 processors. Such extenders allow DOS applications to have total code and data spaces larger than the available base memory, and to have very large code or data objects loaded into memory for enhanced execution speed. The standard configuration of OS/2 Version 2.0 provides both LIM EMS Version 4.0 (which includes backward compatibility with LIM Version 3.X) and LIMA XMS Version 2.0 functions for DOS applications running in virtual DOS machines.
Figure "General Overview of Different Types of Memory for DOS Applications"
This chapter describes the implementation of EMS and XMS support for virtual DOS machines. For those readers not already familiar with the architecture of these memory extenders, an overview is provided in Memory Extender Architectures.