\chapter{Introduction}
\label{ch:introduction}

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Computer systems need to interact with their surroundings, for instance by reading values from sensors, controlling external appliances or interacting with a user through human interface devices.
In each of these scenarios, the system's CPU has to react to \textquote{external changes}, like a key press or sensor reading.
An efficient hardware solution to this problem are \textquote{interrupts}.

Through the past, interrupt hardware went through different iterations: Intel introduced the \textquote{Programmable Interrupt Controller} for the \textquote{8085} processor in 1976, with a revised version for the \textquote{8086} processor.
With modern standards like multicore processors, peripheral extendability, greater flexibility or higher performance, the Programmable Interrupt Controller could no longer meet its requirements.

In this thesis, support for the \textquote{Advanced Programmable Interrupt Controller}, a modern, multiprocessing capable and widely used interrupt controller architecture, introduced by Intel for the x86 \textquote{i486} processor, will be implemented into hhuOS, \textquote{A small operating system for learning purposes}~\autocite{hhuos}.
This support will cover a complete replacement of the older Programmable Interrupt Controller, introduction of an alternative timer -- a part of the APIC architecture -- for scheduling, and utilizing the APIC to boot multiprocessor systems.

The following chapter explains important background concepts, in \autoref{ch:implementation} the required steps to use the APIC and their implementation are explained in general, \autoref{ch:verification} deals with the verification process of the developed software on emulated and real hardware, and \autoref{ch:conclusion} draws conclusions regarding the previous implementation and future improvements.

Specific details on the code created during this thesis are given in \autoref{ch:listings}, separated from the main body.

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