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 can lead to improved performance since communication between components is faster, but it can also make the system more complex and harder to maintain. In contrast to microkernels, which only include essential services in the kernel and run other services in user space, monolithic kernels can be more efficient for certain tasks. Examples of operating systems that use a monolithic kernel include Linux and Unix. These systems benefit from the direct access to hardware and reduced overhead in communication between components.