diff -r 6666fc0b9ebc -r 42c209a6c225 src/Pure/ML-Systems/thread_physical_processors.ML
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/ML-Systems/thread_physical_processors.ML	Wed Dec 11 18:02:22 2013 +0100
@@ -0,0 +1,12 @@
+(*  Title:      Pure/ML-Systems/thread_physical_processors.ML
+    Author:     Makarius
+
+Emulation of structure Thread in Poly/ML 5.5.2 (SVN 1890).
+*)
+
+structure Thread =
+struct
+  open Thread;
+
+  fun numPhysicalProcessors () : int option = NONE;
+end;