LIMSIM LIMSIM

LIMSIM is a relatively easy-to-use commercial program for 286 based and later computers that emulates paged EMS memory using standard 286/386 XMS memory.

EMS memory is a kind of memory expansion used with 8088/8086 CPUs. EMS expansion cards commonly supported multiple megabytes of RAM, but since these CPUs are limited to 1MB of directly accessible RAM, these cards map 64K bytes of memory at a time in to an unused upper memory block within the 1MB addressable space. This was supported by many DOS programs such as Lotus 1-2-3. 286 and 386 computers introduced a new flat addressing scheme (XMS) that could directly access all memory at once (16MB on a 286, 4GB on a 386).

Such EMS simulators usually operated by copying memory back and forth between simulated page buffers allocated within the 640k base memory, and XMS, making them rather slow. This would enable programs that still required EMS to run.