Hardware abstraction

The ISA represents the primitive operations of the machine that are available for use by assembly programmers and compiler writers.

One of the main functions of a compiler is to allow a programmer to write an algorithm in a high-level language without having to care about CPU-specific instructions.

This allows a programmer to use OS-level operations (e.g. task creation/deletion) in their programs while retaining portability over a variety of different platforms.

A "nudge forward" can be from a potentiometer or from a capacitive touch sensor that recognises "swipe" gestures, as long as they both provide a signal related to "movement".

As physical limitations (e.g. resolution of sensor, temporal update frequency) may vary with hardware, an API can do little to hide that, other than by assuming a "least common denominator" model.

The NetBSD operating system is widely known as having a clean hardware abstraction layer which allows it to be highly portable.

Popular buses which are used on more than one architecture are also abstracted, such as ISA, EISA, PCI, PCIe, etc., allowing drivers to also be highly portable with a minimum of code modification.

This was so successful that application software and operating system software above the LIC layer that were compiled on the original S/38 run without modification and without recompilation on the latest AS/400 systems, despite the fact that the underlying hardware has been changed dramatically; at least three different types of processors have been in use.

[6] Android introduced a HAL known as the "vendor interface" (codenamed "Project Treble") on version 8.0 "Oreo".

[8] Halium is an Android-based HAL used by several mobile operating systems such as Ubuntu Touch and LuneOS to run on smartphones with Android pre-installed.