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<chapter id="intro">

  <?dbhtml filename="intro.html" ?>

  <title>Introduction</title>

  <para>HelenOS is a portable operating system with support for a variety of

  modern processor architectures<footnote>

      <para>amd64, arm32, ia32, ia64, mips32, ppc32 and sparc64. ia32xen and

      ppc64 are currently broken.</para>

    </footnote>.</para>

  <para>This book describes the design and principles of the HelenOS operating

  system from the perspective of its microkernel as well as from the

  perspective of its userspace drivers and server tasks. Its primary goal is

  to present ideas behind each subsystem and highlight things that are

  specific to HelenOS. Although this text contains references to source code

  (e.g. function names), these are provided only to improve reader's

  orientation when reading the code. This book does not attempt to be a

  substitute for a reference manual and the reader is strongly encouraged to

  look for interface details there.</para>

  <section>

    <title>How to Read This Book</title>

    <para><xref linkend="architecture" /> contains overview of the overall

    HelenOS architecture.</para>

    <para><xref linkend="ds" /> describes essential data structures used both

    in the kernel and in the userspace.</para>

    <para><xref linkend="time" /> focuses on time management in the kernel and

    scheds some light on the userspace source of time.</para>

    <para><xref linkend="scheduling" /> is dedicated to threads and the

    scheduling subsystem.</para>

    <para><xref linkend="mm" /> describes memory management of physical and

    virtual memory.</para>

    <para><xref linkend="ipc" /> deals with the IPC subsystem.</para>

    <para><xref linkend="hardware" /> describes facilities that a userspace

    task can use in order to become a device driver.</para>

    <para><xref linkend="archspecs" /> presents some architecture specific

    issues.</para>

  </section>

</chapter>