Introduction:
The software built to communicate directly on the hardware is the operating system. It acts as an intermediary between the hardware and the user applications, providing a layer of abstraction and managing the resources of the computer system.

Explanation:
The operating system (OS) is a software program that manages computer hardware and software resources and provides common services for computer programs. It is responsible for the overall operation of the system, including managing the hardware, executing user programs, and providing a user interface.

1. Direct Communication with Hardware:
One of the key responsibilities of an operating system is to provide an interface for applications to communicate directly with the hardware. It abstracts the complexities of the underlying hardware and provides a simplified interface for application developers to interact with the hardware components. This allows applications to utilize the hardware resources efficiently and perform tasks such as reading from and writing to devices, accessing memory, and managing input/output operations.

2. Hardware Abstraction:
The operating system provides a layer of abstraction between the hardware and the user applications. It hides the intricate details of the hardware architecture and presents a uniform interface to the applications. This abstraction allows applications to be hardware-independent, making it easier to develop software that can run on different hardware platforms without significant modifications.

3. Resource Management:
The operating system is responsible for managing the computer's resources, including the processor, memory, and input/output devices. It allocates these resources to different processes and ensures their efficient utilization. The OS also handles resource scheduling and prioritization, ensuring that each process gets a fair share of the available resources.

4. Device Drivers:
Operating systems include device drivers, which are software components that enable communication between the operating system and specific hardware devices. Device drivers act as intermediaries, translating the operating system's requests into commands that the hardware can understand. They provide the necessary software interfaces for applications to interact with the hardware devices.

Conclusion:
In conclusion, the operating system is the software built to communicate directly on the hardware. It provides an interface for applications to interact with the hardware, abstracts the complexities of the hardware architecture, manages system resources, and includes device drivers to facilitate communication with hardware devices.