Internals . Addison Wesley. ISBN 0-201-60835-9 , ISBN 978-0-201-60835-9 . ^ a b c d e Tim Paterson (1983). "An Inside Look at MS-DOS" . Byte . http://www.patersontech.com/dos/Byte/InsideDos.htm#InsideDos_44 . Retrieved 2011-07-18 . "The numbering starts with 2; the first two numbers, 0 and 1, are reserved."   ^ IBM (1984). IBM