diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index c412ee1..5c84e85 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -61,6 +61,13 @@
    names have currently been registered: ``'posix'``, ``'nt'``, ``'mac'``,
    ``'os2'``, ``'ce'``, ``'java'``.
 
+   .. seealso::
+      :attr:`sys.platform` has a finer granularity.  :func:`os.uname` gives
+      system-dependent version information.
+
+      The :mod:`platform` module provides detailed checks for the
+      system's identity.
+
 
 .. _os-filenames:
 
diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst
index ae2dbf3..95dc662 100644
--- a/Doc/library/sys.rst
+++ b/Doc/library/sys.rst
@@ -714,6 +714,12 @@
    For Unix systems, this is the lowercased OS name as returned by ``uname -s``
    with the first part of the version as returned by ``uname -r`` appended,
    e.g. ``'sunos5'`` or ``'linux2'``, *at the time when Python was built*.
+   Unless you want to test for a specific system version, it is therefore
+   recommended to use the following idiom::
+
+      if sys.platform.startswith('linux'):
+          # Linux-specific code here...
+
    For other systems, the values are:
 
    ================ ===========================
@@ -726,6 +732,12 @@
    OS/2 EMX         ``'os2emx'``
    ================ ===========================
 
+   .. seealso::
+      :attr:`os.name` has a coarser granularity.  :func:`os.uname` gives
+      system-dependent version information.
+
+      The :mod:`platform` module provides detailed checks for the
+      system's identity.
 
 .. data:: prefix