diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index 62e4bda..4e41f3f 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -1232,6 +1232,12 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
    :func:`~os.writev` writes the contents of each object to the file descriptor
    and returns the total number of bytes written.
 
+   Buffers are processed in array order. Entire contents of first buffer is
+   written before proceeding to second, and so on.
+
+   The operating system may set a limit (sysconf() value SC_IOV_MAX) on the
+   number of buffers that can be used.
+
    Availability: Unix.
 
    .. versionadded:: 3.3