Explanation of the DEVICE command. It is CONFIG.SYS.

This command will load different devices into your computer's
memory. For a complete list of all the devices that can be 
loaded into your computer's memory please refer to you 
MS-DOS manual.

Example:
       To load the ANSI.SYS device, which is in Drive A into
       your computers memory you would have to include the
       following line in you CONFIG.SYS file:
          device=a:ansi.sys