Abstract: A System Management Mode is transparent to normal system operations and dynamic RAM (DRAM) is available in the Upper Memory Block address range that is normally not accessible in many configurations. Therefore, the DRAM is advantageously used to attain System Management Mode read/write storage requirements. The System Management Mode time-multiplexes the Upper Memory Block memory-mapped address space with other non-DRAM resources in a timely manner by switching the SMM memory into the DRAM Upper Memory Block space in a "just in time" (JIT) basis. The JIT operation is achieved by latching the first memory address emitted from the CPU after SMM entry. The first memory address is designated as the top address of a memory block that extends downward into memory address space, defining an SMM memory range.