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<!--
$FreeBSD$
-->
<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 with a floating point unit
are supported. All
Intel processors beginning with the 80486 are supported, including
the 80486, Pentium, Pentium Pro, Pentium II, Pentium III,
Pentium 4, and variants thereof, such as the Xeon and Celeron
processors. 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
Élan 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 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>
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