freebsd-dev/release/doc/en_US.ISO8859-1/hardware/i386/proc-i386.sgml

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<sect1 id="proc">
  <title>Supported Processors and Motherboards</title>

  <para>&os;/i386 runs on a wide variety of <quote>IBM PC
    compatible</quote> machines.  Due to the wide range of hardware
    available for this architecture, it is impossible to exhaustively
    list all combinations of equipment supported by &os;.
    Nevertheless, some general guidelines are presented here.</para>

  <para>Almost all i386-compatible processors are supported.  All
    Intel processors beginning with the 80386 are supported, including
    the 80386, 80486, Pentium, Pentium Pro, Pentium II, Pentium III,
    Pentium 4, and variants thereof, such as the Xeon and Celeron
    processors.  (However, &os; 5.2-RELEASE and later no longer support
    the 80386SX processor.)  All i386-compatible AMD
    processors are also supported, including the Am486, Am5x86, K5, K6
    (and variants), Athlon (including Athlon-MP, Athlon-XP, Athlon-4,
    and Athlon Thunderbird), and Duron processors.  The AMD
    &Eacute;lan SC520 embedded processor is supported.  The Transmeta
    Crusoe is recognized and supported, as are i386-compatible
    processors from Cyrix and NexGen.</para>

  <para>There is a wide variety of motherboards available for this
    architecture.  Motherboards using the ISA, VLB, EISA, AGP, and PCI
    expansion busses are well-supported.  There is some limited
    support for the MCA (<quote>MicroChannel</quote>) expansion bus
    used in the IBM PS/2 line of PCs.</para>

  <para>Symmetric multi-processor (SMP) systems are generally
    supported by &os;, although in some cases, BIOS or motherboard
    bugs may generate some problems.  Perusal of the archives of the
    &a.smp; may yield some clues.</para>

  <para>&os; will take advantage of HyperThreading (HTT) support on
    Intel CPUs that support this feature.  A kernel with the
    <literal>options&nbsp;SMP</literal> feature enabled will
    automatically detect the additional logical processors.  The
    default &os; scheduler treats the logical processors the same as
    additional physical processors; in other words, no attempt is made
    to optimize scheduling decisions given the shared resources
    between logical processors within the same CPU.  Because this
    naive scheduling can result in suboptimal performance, under
    certain circumstances it may be useful to disable the logical
    processors with the
    the <varname>machdep.hlt_logical_cpus</varname> sysctl variable.
    It is also possible to halt any CPU in the idle loop with the
    <varname>machdep.hlt_cpus</varname> sysctl variable.  The
    &man.smp.4; manual page has more details.</para>

  <para>&os; will take advantage of Physical Address Extensions (PAE)
    support on CPUs that support this feature.  A kernel with the
    <literal>PAE</literal> feature enabled will detect memory above
    4 gigabytes and allow it to be used by the system.  This feature
    places constraints on the device drivers and other features of
    &os; which may be used; consult the &man.pae.4; manpage for more
    details.</para>

  <para>&os; will generally run on i386-based laptops, albeit with
    varying levels of support for certain hardware features such as
    sound, graphics, power management, and PCCARD expansion slots.
    These features tend to vary in idiosyncratic ways between
    machines, and frequently require special-case support in &os; to
    work around hardware bugs or other oddities.  When in doubt, a
    search of the archives of the &a.mobile; may be useful.</para>

  <para>Most modern laptops (as well as many desktops) use the
    Advanced Configuration and Power Management (ACPI) standard.  &os;
    supports ACPI via the ACPI Component Architecture reference
    implementation from Intel, as described in the &man.acpi.4; manual
    page.  The use of ACPI causes instabilities on some machines and it
    may be necessary to disable the ACPI driver, which is normally
    loaded via a kernel module.  This may be accomplished by adding
    the following line to <filename>/boot/device.hints</filename>:</para>

  <programlisting>hint.acpi.0.disabled="1"</programlisting>

  <para>Users debugging ACPI-related problems may find it useful to
    disable portions of the ACPI functionality.  The &man.acpi.4;
    manual page has more information on how to do this via loader
    tunables.</para>

  <para>ACPI depends on a Differentiated System Descriptor Table
    (DSDT) provided by each machine's BIOS.  Some machines have bad or
    incomplete DSDTs, which prevents ACPI from functioning correctly.
    Replacement DSDTs for some machines can be found at the <ulink
    url="http://acpi.sourceforge.net/dsdt/index.php">DSDT</ulink>
    section of the <ulink
    url="http://acpi.sourceforge.net/">ACPI4Linux</ulink> project Web
    site.  &os; can use these DSDTs to override the DSDT provided by
    the BIOS; see the &man.acpi.4; manual page for more
    information.</para>

</sect1>