DOS

http://technet.microsoft.com/en-us/library/bb490890.aspx
http://www.easydos.com/dosindex.html
http://www.uv.tietgen.dk/staff/mlha/pc/soft/dos/com/
http://www.c3scripts.com/tutorials/msdos/commands.html
http://www.computerhope.com/overview.htm