figure 2.15 illustrates the overall structure of windows 7; all releases of windows based on NT have essentially the same structure at this level of detail.
As with virtually all operating systems, Windows separates application-oriented software from the core OS software.The latter, which includes the Executive, the Kernel, device drivers, and hardware abstraction layer, runs in kernel mode.Kernel mode software has access to system data and to the hardware. The remaining software, running in user mod, has limited access to system data.