DIRECTORIES system : compiled versions of the various system components and libraries ntoskrnl : microkernel source ntoskrnl/hal : hardware abstraction layer source ntoskrnl/mm : memory managment subsystem source ntoskrnl/io : IO manager subsystem source include : win32 headers include/internal : kernel private header files include/ntdll : system library private header files include/kernel32 : system library private header files include/user32 : user interface private header files include/gdi32 : graphics interface private header files include/ddk : header files for modules lib/ntdll : NT dll source lib/kernel32 : kernel32 source doc : documentation loaders/dos : DOS based loader loaders/boot : boot loader services : various services (device drivers, filesystems etc)