Prior to the Intel 386 chip, an EMS emulator was a slow, low-cost software alternative to an EMS board. In PC XTs and ATs, it simulated EMS memory in extended memory or on disk. On 386s, it referred to a memory manager (EMM) that created EMS from extended memory. Technically, the 386 architecture did not emulate EMS, it mapped extended memory into the page frame. See
EMS.