http://batman.eng.monash.edu.au/eng1602/tutes/node6.html

http://www.enc.hull.ac.uk/EE/document/msdoslab/msdos/index.htm

http://www.cm.cf.ac.uk/User/P.L.Poulain/project/external.htm

http://www.middlebury.edu/~its/documentation/pcbasics/DosQuickRef.htm