DOS EMM386.EXE 

 
Starting with DOS 5 and Windows 3.0, EMM386.EXE is an expanded memory manager (EMM) for 386s and up, which is software that converts extended memory into EMS memory. It also allows drivers and TSRs to be stored in the upper memory area (UMA) between 640K and 1M.

EMS memory is required by some DOS applications. Most users running Windows and an occasional DOS program do not require it. However, EMM386's ability to store drivers in the UMA helps free up more conventional memory, which is the first 640K of memory. Windows 3.1 relies on DOS for many basic functions, thus freeing up conventional memory is equally as important for Windows 3.1 as it is for a DOS-only system.

In Windows 95/98, EMM386.EXE can still be used to store 16-bit drivers and TSRs in upper memory if required. However, Win 95/98 has its own memory manager that supports EMS memory if DOS applications run windowed rather than full screen.

EMM386 is activated with a statement in the CONFIG.SYS file. The HIMEM.SYS driver must precede EMM386.EXE:


          device=himem.sys
          device=emm386.exe



To provide access to the UMA, either the RAM or NOEMS parameters must be added:


      device=emm386.exe noems    UMA only
      device=emm386.exe ram      UMA and EMS



The default amount of memory used is 256K, but you can allocate from 16 to 32768K, for example:


     device=emm386.exe 1300 ram



For DOS 6 Users: The EMM386.EXE that comes with DOS 6 can dynamically convert extended memory into EMS memory when an application requires it. To free up all of extended memory until some of it is required for your EMS application, type:


     device=emm386.exe min=0 ram




EMM386.EXE is an executable program, which can be run after it has been initialized in order to change settings. For example, you can turn off EMS memory management by typing:


           emm386 off     turn it off

           emm386 on      turn it back on