The following is a map of memory usage while the OS/2 subsystem is running an application.
Figure 28.1 OS/2 Subsystem Memory Map
The tiled area is 512 MB of virtual address space that is reserved up-front and then committed or decommitted when 16-bit applications need segments. The OS/2 subsystem maintains a local descriptor table (LDT) for each process, with shared memory segments at the same LDT slot for all OS/2 processes.