--- make.conf	2006-03-19 18:40:11.000000000 +0100
+++ make.conf.amd64	2006-03-19 18:26:21.000000000 +0100
@@ -23,6 +23,11 @@
 # Example:
 #USE="X gtk gnome -alsa"
 
+# Host Setting
+# ============
+#
+CHOST="x86_64-pc-linux-gnu"
+
 # Host and optimization settings 
 # ==============================
 #
@@ -33,10 +38,35 @@
 # package (and in some cases the libraries it uses) at default optimizations
 # before reporting errors to developers.
 #
-# Please refer to the GCC manual for a list of possible values.
+# -mcpu=<cpu-type> means optimize code for the particular type of CPU without
+# breaking compatibility with other CPUs. GCC 3.4 has deprecated support for
+# -mcpu, so use -mtune instead if using this compiler.
+#
+# -march=<cpu-type> means to take full advantage of the ABI and instructions
+# for the particular CPU; this will break compatibility with older CPUs (for
+# example, -march=athlon-xp code will not run on a regular Athlon, and
+# -march=i686 code will not run on a Pentium Classic.)
+#
+# CPU types supported in gcc-3.2 and higher: athlon-xp, athlon-mp,
+# athlon-tbird, athlon, k6, k6-2, k6-3, i386, i486, i586 (Pentium), i686
+# (PentiumPro), pentium, pentium-mmx, pentiumpro, pentium2 (Celeron),
+# pentium3, and pentium4.
+#
+# Note that Gentoo Linux 1.4 and higher include at least gcc-3.2.
+#
+# amd64 CPU types supported in gcc-3.4: athlon64, opteron, k8
+# 
+# CRITICAL WARNINGS: ****************************************************** #
+# K6 markings are deceptive. Avoid setting -march for them. See Bug #24379. #
+# Pentium-M CPUs should not enable sse2 until at least gcc-3.4. Bug 50616. #
+# GCC 3.3 doesnt support an amd64 specific -march setting, use 3.4.         #
+# ************************************************************************* #
 #
-#CFLAGS="-O2 -pipe"
+# Decent examples:
 #
+#CFLAGS="-mtune=k8 -O2 -pipe"
+#CFLAGS="-march=athlon64 -O2 -pipe"
+
 # If you set a CFLAGS above, then this line will set your default C++ flags to
 # the same settings.
 #CXXFLAGS="${CFLAGS}"
@@ -61,7 +91,7 @@
 # DO NOT PUT ANYTHING BUT YOUR SPECIFIC ~ARCHITECTURE IN THE LIST.
 # IF YOU ARE UNSURE OF YOUR ARCH, OR THE IMPLICATIONS, DO NOT MODIFY THIS.
 #
-#ACCEPT_KEYWORDS="~arch"
+#ACCEPT_KEYWORDS="~amd64"
 
 # Portage Directories
 # ===================