Index: book.sgml
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RCS file: /home/dcvs/doc/en_US.ISO8859-1/books/faq/book.sgml,v
retrieving revision 1.1065
diff -u -r1.1065 book.sgml
--- book.sgml	6 Jul 2008 09:19:23 -0000	1.1065
+++ book.sgml	10 Jul 2008 12:31:14 -0000
@@ -2106,6 +2106,68 @@
     </qandaset>
       </sect1>
 
+      <sect1 id="compatibility-memory">
+        <title>Memory</title>
+        <qandaset>
+          <qandaentry>
+          <question id="memory">
+            <para>Does FreeBSD support more than 4 GB of memory (RAM)? More 
+              than 16 GB? More than 48 GB?</para>
+          </question>
+          <answer>
+            <para>
+            Yes. FreeBSD as an operating system generally supports as much
+            physical memory (RAM) as the platform it's running on does. Keep in
+            mind that different platforms have different limits for memory;
+            for example: i386 without PAE supports at most 4 GB of memory
+            (and usually less than that), i386 with PAE supports at most
+            64 GB memory. AMD64 platforms currently deployed support up to
+            1 TB of physical memory.
+            </para>
+          </answer>
+          </qandaentry>
+
+          <qandaentry>
+          <question id="i386memory">
+            <para>Why does FreeBSD report less than 4 GB memory when installed
+              on a i386 machine?</para>
+          </question>
+          <answer>
+            <para>
+            The total address space on i386 machines is 32-bit, meaning that at
+            most 4 GB of memory is addressible (can be accessed). From this
+            range, some addresses are reserved by hardware for different purposes,
+            for example for using and controlling PCI devices, for accessing
+            video memory, etc., limiting the total memory usable by the 
+            operating system for its kernel and applications to significantly
+            less than 4 GB. Usually, 3.2 GB to 3.7 GB is the maximum usable
+            physical memory in this configuration.
+            </para>
+            <para>
+            To access more than 3.2 GB to 3.7 GB of installed memory (meaning
+            up to 4 GB but also more than 4 GB), a special tweak called "PAE"
+            must be used. PAE stands for Physical Address Extension and is a
+            way for 32-bit x86 CPUs to address more than 4 GB of memory. It
+            remaps the memory that would otherwise be overlayed by address
+            reservations for hardware devices above the 4 GB range and uses it
+            as additional physical memory (see &man.pae.4;). Using PAE has
+            some drawbacks: this mode of memory access is a little bit slower
+            than the "normal" mode and loadable modules (see &man.kld.4;) are
+            not supported (meaning all drivers must be compiled into the
+            kernel proper).
+            </para>
+            <para>
+            PAE is not much used nowadays because most new x86 hardware also
+            supports running in 64-bit mode (AMD64), which has a much larger
+            address space and doesn't need such tweaks. FreeBSD supports AMD64
+            and it's recommended that this version of FreeBSD be used instead
+            of the i386 version if 4 GB or more memory is required.
+            </para>
+          </answer>
+          </qandaentry>
+        </qandaset>
+      </sect1>
+
       <sect1 id="compatibility-processors">
 	<title>Architectures and processors</title>