diff --git a/doc/card_bdata.md b/doc/card_bdata.md
new file mode 100644
index 0000000..af66530
--- /dev/null
+++ b/doc/card_bdata.md
@@ -0,0 +1,18 @@
+# Card Bdata table
+
+Stores some binary card data, encoded in base64
+
+| index | size | data                                      |
+| ----- | ---- | ----------------------------------------- |
+| 0     | 6    | fixed value "1.51"                        |
+| 1     | 6    | Last played song and difficulty?          |
+| 2     | 68   | Something consist of 17 ints              |
+| 3     | 4    | Start related, unknown                    |
+| 4     | 4    | Something whose max value is 100, unknown |
+| 5     | 4    | Unknown                                   |
+| 6     | 4    | Unknown                                   |
+| 7     | 4    | Unknown                                   |
+| 8     | 4    | Always 0                                  |
+| 9     | 160  | 40 previously newly played song id        |
+| 10    | 16   | Filetime + stamp count                    |
+