All ABAP programs are executed using ABAP Kernel. To understand how ABAP programs are executed and communicate let us first try to understand about Kernels.

In modern computer science world, the kernel is defined as the central component of any operating system. It is responsible for managing the system's resources like CPU, memory, communication with I/O devices etc. A kernel is very basic component of the operating system. It provides the lowest level of abstraction layer for the resources. The below image explains the functionality of a kernel.

Functions of Kernel:

• Kernel is responsible for deciding at any point which program (many programs could run parallely) should be allocated to the processor (and which processor, if more than one are available).
• All programs use memory - to store data and process instructions. Often multiple programs will want access to memory. Th job of kernel is to decide which process should use memory and what to do if enough memory is not available.
• Almost all programs interact with input / output devices like monitor, key board, mouse etc. The kernel allocates these requests to appropriate devices or sub section of devices.