A monolithic kernel is a type of operating system architecture where the entire operating system runs as a single program in a single address space. This means that all core services, such as device drivers, file management, and system calls, are included in the kernel itself. This design allows for efficient communication between components, as they can directly access each other's functions without needing to go through additional layers. In contrast to microkernels, which separate services into distinct processes, monolithic kernels can lead to better performance due to reduced overhead. However, this design can also make the system more complex and harder to maintain, as a bug in one part of the kernel can potentially crash the entire system. Examples of operating systems that use a monolithic kernel include Linux and Unix.