The DEVICE line loads device drivers. EMM386 is a device driver which needs to be started very early in the DOS boot process for it to work -- because most of

The DEVICE line loads device drivers. EMM386 is a device driver which needs to be started very early in the DOS boot process for it to work -- because most of the rest of DOS is then loaded into memory blocks that EMM386 provides. It's an .EXE file because the command invocation gives some useful data -- but it can't load that way, and if it could it would be useless because then it was too late to load drivers into the memory regions it created.