Many operating systems are not based on one model of the operating system. They may contain multiple operating systems that have different approaches to performance, security, usability needs etc. This is known as a hybrid operating system.
The Hybrid operating system may allow one operating system to fulfil one set of requirements and the other operating system to fulfil the rest. For example, one of the operating systems may provide user interface, applications monitoring etc. while the other operating system may be a high-performance operating system that does not provide the same services as the first operating system.
Some of the important features of the hybrid operating system are as follows:
The kernel is the core part of the operating system as it manages the operations of the computer as well as the hardware. The hybrid kernel attempts to combine the features and aspects of the microkernel and the monolithic kernel. This means that the kernel structure should be similar to a microkernel but the structure should be implemented like a monolithic kernel.
A well-known example of the hybrid kernel is the Microsoft Windows NT kernel. This kernel handles all the operating systems in the Windows NT family. It is called a hybrid kernel instead of a monolithic kernel as the emulation subsystems run on the user mode rather than the kernel mode, unlike in monolithic kernel.
The NT kernel cannot be called a microkernel as well. This is because almost all the system components run on the same address space as the kernel, which is a feature of the monolithic kernel.
A figure that illustrates the structure of the Microsoft Windows NT kernel is as follows:
There are mainly two layers in the Windows NT operating system architecture i.e user mode and kernel mode. The user mode contains the Integral Subsystems and Environmental Subsystems with various modules in each of them.
The executive part of the kernel mode contains the executive services and object manager. The executive services include I/O manager, IPC manager, process manager etc.
Apart from the executive mode, the kernel mode contains the kernel mode drivers, the microkernel and the hardware abstraction layer. The hardware abstraction layer is connected to the hardware.