diff --git a/src/com/bytezone/diskbrowser/cpm/CPMDisk.java b/src/com/bytezone/diskbrowser/cpm/CPMDisk.java
index ddcd478..ac04f0e 100644
--- a/src/com/bytezone/diskbrowser/cpm/CPMDisk.java
+++ b/src/com/bytezone/diskbrowser/cpm/CPMDisk.java
@@ -16,6 +16,7 @@ import com.bytezone.diskbrowser.disk.SectorType;
 import com.bytezone.diskbrowser.gui.DataSource;
 import com.bytezone.diskbrowser.utilities.HexFormatter;
 
+// https://www.retrotechnology.com/dri/howto_cpm.html
 // -----------------------------------------------------------------------------------//
 public class CPMDisk extends AbstractFormattedDisk
 // -----------------------------------------------------------------------------------//