A thin layer of software at the base of the Microsoft Windows NT and Windows 2000 operating systems that offers a uniform interface between the underlying hardware and the higher layers of the operating system, hiding hardware differences from those higher layers. In other words, the hardware abstraction layer (HAL) hides hardware differences from the operating system so that uniform code can be used for all hardware. All hardware looks the same to the operating system because it “sees” the hardware through the filtered glasses of the HAL.
The HAL is located at the base of the Executive Services, and it encapsulates most hardware-specific functions that are performed by the operating system. If another portion of the operating system wants to access a hardware device, it must refer its request to the HAL. The HAL handles communication between the kernel of the operating system and the hardware.
The HAL is implemented in Windows as a file called hal.dll. If a hardware vendor needs to protect proprietary technology, the company can develop a custom implementation of the HAL. This means that different processor configurations might use different HAL drivers.