- The kernel, or core, of the OS is responsible for interacting with hardware. Because the kernel operates in kernel mode, it has more power to communicate with hardware devices than the shell has. Applications operating under the OS cannot get to hardware devices without the shell passing those requests to the kernel. This separation of tasks provides for a more stable system and helps to prevent a wayward application from destabilizing the system. - The kernel has two main components: 1) the HAL (hardware abstraction layer), which is the layer closest to the hardware, and 2) the executive services interface, which is a group of services that operate in kernel mode between the user mode subsystems and the HAL. Executive services contained in the ntoskrnl.exe program file manage memory, I/O devices, file systems, some security, and other key components directly or by way of device drivers. When Windows is first installed, it builds the HAL based on the type of CPU installed. The HAL cannot be moved from one computer to another, which is one reason you cannot copy a Windows installation from one computer to another.