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diff --git a/system/doc/efficiency_guide/advanced.xml b/system/doc/efficiency_guide/advanced.xml
index 51f1b2612c..ed7a6670ed 100644
--- a/system/doc/efficiency_guide/advanced.xml
+++ b/system/doc/efficiency_guide/advanced.xml
@@ -199,6 +199,31 @@ On 64-bit architectures: 4 words for a reference from the current local node, an
available, and operating system specific settings and limits.</item>
<tag><em>Number of arguments to a function or fun</em></tag>
<item>255</item>
+ <tag><marker id="unique_references"/><em>Unique References on a Runtime System Instance</em></tag>
+ <item>Each scheduler thread has its own set of references, and all
+ other threads have a shared set of references. Each set of references
+ consist of <c>2⁶⁴ - 1</c> unique references. That is the total
+ amount of unique references that can be produced on a runtime
+ system instance is <c>(NoSchedulers + 1) * (2⁶⁴ - 1)</c>. If a
+ scheduler thread create a new reference each nano second,
+ references will at earliest be reused after more than 584 years.
+ That is, for the foreseeable future they are unique enough.</item>
+ <tag><marker id="unique_integers"/><em>Unique Integers on a Runtime System Instance</em></tag>
+ <item>There are two types of unique integers both created using the
+ <seealso marker="erts:erlang#unique_integer/1">erlang:unique_integer()</seealso>
+ BIF. Unique integers created:
+ <taglist>
+ <tag><em>with</em> the <c>monotonic</c> modifier</tag>
+ <item>consist of a set of <c>2⁶⁴ - 1</c> unique integers.</item>
+ <tag><em>without</em> the <c>monotonic</c> modifier</tag>
+ <item>consist of a set of <c>2⁶⁴ - 1</c> unique integers per scheduler
+ thread and a set of <c>2⁶⁴ - 1</c> unique integers shared by
+ other threads. That is the total amount of unique integers without
+ the <c>monotonic</c> modifier is <c>(NoSchedulers + 1) * (2⁶⁴ - 1)</c></item>
+ </taglist>
+ If a unique integer is created each nano second, unique integers
+ will at earliest be reused after more than 584 years. That is, for
+ the foreseeable future they are unique enough.</item>
</taglist>
</section>
</chapter>