--- a/Sphinx/source/faq/features.rst	Fri Feb 26 08:35:52 2021 +0100
+++ b/Sphinx/source/faq/features.rst	Fri Feb 26 09:00:27 2021 +0100
@@ -234,6 +234,11 @@
 ``OrthancPluginSetGlobalProperty()``) are therefore kindly invited to
 complete the **central registry** below:
 
+* ``Attachment 1`` is used by the core of Orthanc to store DICOM instances
+* ``Attachment 2`` was used by Orthanc <= 1.9.0 to cache the :ref:`DICOM-as-JSON information <orthanc-storage>`
+* ``Attachment 3`` is used since Orthanc 1.9.1 to store the DICOM instance, until the ``Pixel Data (7fe0,0010)`` tag,
+  if global configuration option ``StorageCompression`` is ``true``, or if the storage area plugin doesn't support
+  range reads
 * ``Attachment 9997`` is used by the :ref:`Osimis WebViewer plugin <osimis_webviewer>` to store series information.
 * ``Attachment 9998`` is used by the :ref:`Osimis WebViewer plugin <osimis_webviewer>` to store instance information.
 * ``Attachment 9999`` is used by the :ref:`Osimis WebViewer plugin <osimis_webviewer>` to store annotations.