What is the X in X-mas?
Memory used through EMS. In systems based on Intel 80386 or later processor expanded memory is part of the extended memory that is mapped into the expanded memory page frame by the processor. The mapping is controlled by the EMM. In earlier systems, a dedicated EMS hardware adaptor is needed to map memory into the page frame. In both cases, an appropriate device driver is needed for the proper communication between hardware and EMM.