An operating system interfaces with hardware's firmware through:

The interface between an operating system and hardware firmware is primarily facilitated by device drivers. Device drivers are specialized software components that allow the operating system to communicate with hardware devices. They serve as translators, enabling the OS to interact with hardware components by hiding the complexity of the hardware from the OS and applications.

When the operating system needs to perform operations on a hardware device, it sends commands to the device driver, which then translates those commands into a format that the hardware can understand. In essence, device drivers are essential for the proper functioning of hardware components, such as printers, graphics cards, and network adapters, within the operating system environment.

Kernels, while they play a foundational role within the operating system by managing system resources and communication between hardware and software, do not directly interface with firmware. Applications operate at a higher level and rely on the operating system and device drivers to function with hardware. The keyboard, on the other hand, is a specific type of hardware rather than a component that facilitates communication between the OS and all hardware firmware.