diff --git a/netbox_agent/inventory.py b/netbox_agent/inventory.py
index 68ec164..4a1fd65 100644
--- a/netbox_agent/inventory.py
+++ b/netbox_agent/inventory.py
@@ -1,8 +1,8 @@
 import subprocess
 import re
-from shutil import which
 
 from netbox_agent.config import netbox_instance as nb
+from netbox_agent.misc import is_tool
 from netbox_agent.raid.hp import HPRaid
 from netbox_agent.raid.dell import StorcliRaid
 import netbox_agent.dmidecode as dmidecode
@@ -25,39 +25,23 @@ for key, tag in INVENTORY_TAG.items():
             comments=tag['name'],
             )
 
-
-def is_tool(name):
-    '''Check whether `name` is on PATH and marked as executable.'''
-    return which(name) is not None
-        
-class DictDiffer(object):
-    """
-    Calculate the difference between two dictionaries as:
-    (1) items added
-    (2) items removed
-    (3) keys same in both but changed values
-    (4) keys same in both and unchanged values
-    """
-
-    def __init__(self, current_dict, past_dict):
-        self.current_dict, self.past_dict = current_dict, past_dict
-        self.set_current, self.set_past = set(current_dict.keys()), set(past_dict.keys())
-        self.intersect = self.set_current.intersection(self.set_past)
-        
-    def added(self):
-        return self.set_current - self.intersect
-    def removed(self):
-        return self.set_past - self.intersect
-    def changed(self):
-        return set(o for o in self.intersect if self.past_dict[o] != self.current_dict[o])
-    def unchanged(self):
-        return set(o for o in self.intersect if self.past_dict[o] == self.current_dict[o])
-
 class Inventory():
     """
     Better Inventory items coming, see:
     - https://github.com/netbox-community/netbox/issues/3087
     - https://github.com/netbox-community/netbox/issues/3333
+
+    This class implements for:
+    * memory
+    * cpu
+    * raid cards
+    * disks
+
+    methods that:
+    * get local item
+    * get netbox item
+    * create netbox item
+    * update netbox item
     """
 
     def __init__(self, server):
@@ -65,7 +49,6 @@ class Inventory():
         self.device_id = self.server.get_netbox_server().id
         self.raid = None
         self.disks = []
-        self.memories = []
 
     def get_cpus(self):
         model = None
@@ -104,7 +87,7 @@ class Inventory():
         controllers = self.raid.get_controllers()
         if len(self.raid.get_controllers()):
             return self.raid.get_controllers()
-        
+
     def get_netbox_raid_cards(self):
         raid_cards = nb.dcim.inventory_items.filter(
             device_id=self.device_id,
@@ -137,7 +120,7 @@ class Inventory():
             name='{}'.format(raid_card.get_product_name()),
             serial='{}'.format(raid_card.get_serial_number()),
         )
-        
+
     def create_netbox_raid_cards(self):
         for raid_card in self.get_raid_cards():
             self.create_netbox_raid_card(raid_card)
@@ -153,7 +136,7 @@ class Inventory():
         We only need to handle destroy and new cards
         """
 
-        nb_raid_cards = self.get_netbox_raid_cards()        
+        nb_raid_cards = self.get_netbox_raid_cards()
         raid_cards = self.get_raid_cards()
 
         # delete cards that are in netbox but not locally
diff --git a/netbox_agent/misc.py b/netbox_agent/misc.py
new file mode 100644
index 0000000..1142745
--- /dev/null
+++ b/netbox_agent/misc.py
@@ -0,0 +1,5 @@
+from shutil import which
+
+def is_tool(name):
+    '''Check whether `name` is on PATH and marked as executable.'''
+    return which(name) is not None