The 2MB EMS Board utilises up to four AS6C4008-55SIN 4Mb static RAM chips to provide up to 16Mb (=2MB) total RAM capacity, buffered via a 74ACT245 to ensure compatibility with TTL logic levels, on an 8-bit ISA expansion card. For applications that support EMS, this provides a way to install more than the 1MB total address capacity of the 8086 and 8088 processors.
Following the LIM EMS specification, physical RAM is divided into 16KB pages and addressed via a single 64KB window (the ‘page frame’) in the upper memory. The pages presented within the window are determined by the value set in four page registers, which are programmed through IO ports. A jumper block enables the page frame IO port base addresses to configured to match the system requirements.
For operation, the EMS board requires a LIM memory manager driver, LTEMM.EXE. This driver provides LIM 4 compatibility.