The kernel is the (66) of an operating system such as Windows98, Windows NT, Mac OS or Unix. The kernel provides basic services for the other parts of the operating system, (67) it possible for it to run several programs at once (multitasking), read and write files and connect to networks and peripherals. Applications and utility programs use the services provided by the kernel to provide practical business functionality.
In operating systems such as Windows or most versions of Unix, the kernel (68) everything except application and utility programs.
In microkernel operating systems such as Digital Unix and Apples forthcoming Mac OS Server, the kernel (69) supports only multitasking and memory management. Other services such as applications, utilities and the user interface support device drivers, API and graphics which all (70) outside the microkernel.
（66）处填（）。
A．nucleus
B．center
C．core
D．heart
