The memory between 640KB and 1MB is called high-end memory, which is reserved for use by the system. The memory above 1MB becomes the extended memory, and the extended memory is managed by HIMEM.SYS.
EMM386.EXE is responsible for managing high-end memory and simulating the extended memory in the extended memory for use by some software.
Therefore, in order to use more memory, the following instructions should be in the setup file under DOS.
DEVICE=C:\DOS\EMM386.EXE RAM
It should be noted that: EMM386.EXE must first install HIMEM.SYS, so you must ensure that the configuration of HIMEM.SYS is installed The command comes before EMM386.EXE.
Win95 and later systems no longer need this program.