OS mappable window
In addition to the normal mappable window, additional memory below 1MB can also be remapped. This is typically all memory from 256KB to 640KB. This is used by task management programs (such as Microsoft Windows) to map a different section of expanded memory to this region for each application it runs. An application can, however, remap this memory. No protection is provided. This memory is automatically allocated to a special handle and is mapped when EMS starts, before the operating system touches the memory.