diff --git a/spinn_machine/multicast_routing_entry.py b/spinn_machine/multicast_routing_entry.py
index 755a9fff..af06ec8d 100644
--- a/spinn_machine/multicast_routing_entry.py
+++ b/spinn_machine/multicast_routing_entry.py
@@ -14,8 +14,12 @@
 from __future__ import annotations
 from typing import Any, FrozenSet, Iterable, Optional, Tuple, overload
 from spinn_machine.router import Router
+from spinn_machine.data import MachineDataView
 from .exceptions import SpinnMachineInvalidParameterException
 
+# cache of MachineDataView.get_machine_version().max_cores_per_chip
+max_cores_per_chip: int = 0
+
 
 class MulticastRoutingEntry(object):
     """
@@ -74,6 +78,10 @@ def __init__(self, routing_entry_key: int, mask: int, *,
         :raise TypeError: if no spinnaker_route provided and either
             processor_ids or link_ids is missing or `None`
         """
+        global max_cores_per_chip
+        if max_cores_per_chip == 0:
+            max_cores_per_chip = \
+                MachineDataView.get_machine_version().max_cores_per_chip
         self._routing_entry_key: int = routing_entry_key
         self._mask: int = mask
         self._defaultable: bool = defaultable
@@ -271,7 +279,7 @@ def _calc_routing_ids(self) -> Tuple[FrozenSet[int], FrozenSet[int]]:
 
         :rtype: tuple(frozenset(int), frozenset(int))
         """
-        processor_ids = (pi for pi in range(0, Router.MAX_CORES_PER_ROUTER)
+        processor_ids = (pi for pi in range(0, max_cores_per_chip)
                          if self._spinnaker_route & 1 <<
                          (Router.MAX_LINKS_PER_ROUTER + pi))
         link_ids = (li for li in range(0, Router.MAX_LINKS_PER_ROUTER)
diff --git a/spinn_machine/router.py b/spinn_machine/router.py
index d634d748..6ddd8dfd 100644
--- a/spinn_machine/router.py
+++ b/spinn_machine/router.py
@@ -14,6 +14,7 @@
 from __future__ import annotations
 from typing import (
     Dict, Iterable, Iterator, List, Optional, Tuple, Union, TYPE_CHECKING)
+from spinn_machine.data import MachineDataView
 from .exceptions import (
     SpinnMachineAlreadyExistsException, SpinnMachineInvalidParameterException)
 if TYPE_CHECKING:
@@ -21,6 +22,9 @@
     from .fixed_route_entry import FixedRouteEntry
     from .multicast_routing_entry import MulticastRoutingEntry
 
+# cache of MachineDataView.get_machine_version().max_cores_per_chip
+max_cores_per_chip: int = 0
+
 
 class Router(object):
     """
@@ -50,6 +54,10 @@ def __init__(
         :raise ~spinn_machine.exceptions.SpinnMachineAlreadyExistsException:
             If any two links have the same ``source_link_id``
         """
+        global max_cores_per_chip
+        if max_cores_per_chip == 0:
+            max_cores_per_chip = \
+                MachineDataView.get_machine_version().max_cores_per_chip
         self._links: Dict[int, Link] = dict()
         for link in links:
             self.add_link(link)
@@ -178,7 +186,7 @@ def convert_spinnaker_route_to_routing_ids(route: int) -> Tuple[
         :return: The list of processor IDs, and the list of link IDs.
         :rtype: tuple(list(int), list(int))
         """
-        processor_ids = [pi for pi in range(0, Router.MAX_CORES_PER_ROUTER)
+        processor_ids = [pi for pi in range(0, max_cores_per_chip)
                          if route & 1 << (Router.MAX_LINKS_PER_ROUTER + pi)]
         link_ids = [li for li in range(0, Router.MAX_LINKS_PER_ROUTER)
                     if route & 1 << li]