diff --git a/MMTk/src/org/mmtk/plan/semispace/usePrimitiveWriteBarriers/UsePrimitiveWriteBarriers.java b/MMTk/src/org/mmtk/plan/semispace/usePrimitiveWriteBarriers/UsePrimitiveWriteBarriers.java
new file mode 100644
index 0000000..92dd225
--- /dev/null
+++ b/MMTk/src/org/mmtk/plan/semispace/usePrimitiveWriteBarriers/UsePrimitiveWriteBarriers.java
@@ -0,0 +1,26 @@
+/*
+ *  This file is part of the Jikes RVM project (http://jikesrvm.org).
+ *
+ *  This file is licensed to You under the Eclipse Public License (EPL);
+ *  You may not use this file except in compliance with the License. You
+ *  may obtain a copy of the License at
+ *
+ *      http://www.opensource.org/licenses/eclipse-1.0.php
+ *
+ *  See the COPYRIGHT.txt file distributed with this work for information
+ *  regarding copyright ownership.
+ */
+package org.mmtk.plan.semispace.usePrimitiveWriteBarriers;
+
+import org.mmtk.plan.semispace.SS;
+
+import org.vmmagic.pragma.*;
+
+/**
+ * This class exercises primitive write barriers The write barriers contain no
+ * payloads but merely perform a write to the heap
+ */
+@Uninterruptible
+public class UsePrimitiveWriteBarriers extends SS {
+
+}
diff --git a/MMTk/src/org/mmtk/plan/semispace/usePrimitiveWriteBarriers/UsePrimitiveWriteBarriersCollector.java b/MMTk/src/org/mmtk/plan/semispace/usePrimitiveWriteBarriers/UsePrimitiveWriteBarriersCollector.java
new file mode 100644
index 0000000..773e9a5
--- /dev/null
+++ b/MMTk/src/org/mmtk/plan/semispace/usePrimitiveWriteBarriers/UsePrimitiveWriteBarriersCollector.java
@@ -0,0 +1,25 @@
+/*
+ *  This file is part of the Jikes RVM project (http://jikesrvm.org).
+ *
+ *  This file is licensed to You under the Eclipse Public License (EPL);
+ *  You may not use this file except in compliance with the License. You
+ *  may obtain a copy of the License at
+ *
+ *      http://www.opensource.org/licenses/eclipse-1.0.php
+ *
+ *  See the COPYRIGHT.txt file distributed with this work for information
+ *  regarding copyright ownership.
+ */
+package org.mmtk.plan.semispace.usePrimitiveWriteBarriers;
+
+import org.mmtk.plan.semispace.SSCollector;
+import org.vmmagic.pragma.*;
+
+/**
+ * This class extends the {@link SSCollector} class as part of the
+ * {@link UsePrimitiveWriteBarriers} collector. All implementation details
+ * concerning GC are handled by {@link SSCollector}
+ */
+@Uninterruptible
+public class UsePrimitiveWriteBarriersCollector extends SSCollector {
+}
diff --git a/MMTk/src/org/mmtk/plan/semispace/usePrimitiveWriteBarriers/UsePrimitiveWriteBarriersConstraints.java b/MMTk/src/org/mmtk/plan/semispace/usePrimitiveWriteBarriers/UsePrimitiveWriteBarriersConstraints.java
new file mode 100644
index 0000000..128406b
--- /dev/null
+++ b/MMTk/src/org/mmtk/plan/semispace/usePrimitiveWriteBarriers/UsePrimitiveWriteBarriersConstraints.java
@@ -0,0 +1,27 @@
+/*
+ *  This file is part of the Jikes RVM project (http://jikesrvm.org).
+ *
+ *  This file is licensed to You under the Eclipse Public License (EPL);
+ *  You may not use this file except in compliance with the License. You
+ *  may obtain a copy of the License at
+ *
+ *      http://www.opensource.org/licenses/eclipse-1.0.php
+ *
+ *  See the COPYRIGHT.txt file distributed with this work for information
+ *  regarding copyright ownership.
+ */
+package org.mmtk.plan.semispace.usePrimitiveWriteBarriers;
+
+import org.mmtk.plan.semispace.SSConstraints;
+import org.vmmagic.pragma.*;
+
+/**
+ * UsePrimitiveWriteBarriers common constants.
+ */
+@Uninterruptible
+public class UsePrimitiveWriteBarriersConstraints extends SSConstraints {
+
+  /** @return True if this Plan requires primitive write barriers. */
+  @Override
+  public boolean needsPrimitiveWriteBarrier() { return true; }
+}
diff --git a/MMTk/src/org/mmtk/plan/semispace/usePrimitiveWriteBarriers/UsePrimitiveWriteBarriersMutator.java b/MMTk/src/org/mmtk/plan/semispace/usePrimitiveWriteBarriers/UsePrimitiveWriteBarriersMutator.java
new file mode 100644
index 0000000..8df47a5
--- /dev/null
+++ b/MMTk/src/org/mmtk/plan/semispace/usePrimitiveWriteBarriers/UsePrimitiveWriteBarriersMutator.java
@@ -0,0 +1,168 @@
+/*
+ *  This file is part of the Jikes RVM project (http://jikesrvm.org).
+ *
+ *  This file is licensed to You under the Eclipse Public License (EPL);
+ *  You may not use this file except in compliance with the License. You
+ *  may obtain a copy of the License at
+ *
+ *      http://www.opensource.org/licenses/eclipse-1.0.php
+ *
+ *  See the COPYRIGHT.txt file distributed with this work for information
+ *  regarding copyright ownership.
+ */
+package org.mmtk.plan.semispace.usePrimitiveWriteBarriers;
+
+import org.mmtk.plan.semispace.SSMutator;
+import org.mmtk.vm.VM;
+
+import org.vmmagic.unboxed.*;
+import org.vmmagic.pragma.*;
+
+/**
+ * This class extends the {@link SSMutator} class as part of the
+ * {@link UsePrimitiveWriteBarriers} collector. It overrides various methods in
+ * {@link Mutator} to implement primitive write barriers.
+ */
+@Uninterruptible
+public class UsePrimitiveWriteBarriersMutator extends SSMutator {
+
+  /****************************************************************************
+   *
+   * Primitive Write Barrier specific
+   */
+
+  /**
+   * A boolean needs to be written into an object
+   * @param src The object into which the new primitive will be stored
+   * @param slot The address into which the new primitive will be stored.
+   * @param value The new boolean (byte)
+   * @param metaDataA A value that assists the host VM in creating a store
+   * @param metaDataB A value that assists the host VM in creating a store
+   * @param mode The mode of the store (eg putfield, putstatic etc)
+   */
+  @Inline
+  public final void writeBarrier(ObjectReference src, Address slot,
+                                 boolean value, Word metaDataA, Word metaDataB, int mode) {
+    VM.barriers.performWriteInBarrier(src, slot, value, metaDataA, metaDataB, mode);
+  }
+
+  /**
+   * A byte needs to be written into an object
+   * @param src The object into which the new primitive will be stored
+   * @param slot The address into which the new primitive will be stored.
+   * @param value The new byte
+   * @param metaDataA A value that assists the host VM in creating a store
+   * @param metaDataB A value that assists the host VM in creating a store
+   * @param mode The mode of the store (eg putfield, putstatic etc)
+   */
+  @Inline
+  public final void writeBarrier(ObjectReference src, Address slot,
+                                 byte value, Word metaDataA, Word metaDataB, int mode) {
+    VM.barriers.performWriteInBarrier(src, slot, value, metaDataA, metaDataB, mode);
+  }
+
+  /**
+   * A char needs to be written into an object
+   * @param src The object into which the new primitive will be stored
+   * @param slot The address into which the new primitive will be stored.
+   * @param value The new char
+   * @param metaDataA A value that assists the host VM in creating a store
+   * @param metaDataB A value that assists the host VM in creating a store
+   * @param mode The mode of the store (eg putfield, putstatic etc)
+   */
+  @Inline
+  public final void writeBarrier(ObjectReference src, Address slot,
+                                 char value, Word metaDataA, Word metaDataB, int mode) {
+    VM.barriers.performWriteInBarrier(src, slot, value, metaDataA, metaDataB, mode);
+  }
+
+  /**
+   * A double needs to be written into an object
+   * @param src The object into which the new primitive will be stored
+   * @param slot The address into which the new primitive will be stored.
+   * @param value The new double
+   * @param metaDataA A value that assists the host VM in creating a store
+   * @param metaDataB A value that assists the host VM in creating a store
+   * @param mode The mode of the store (eg putfield, putstatic etc)
+   */
+  @Inline
+  public final void writeBarrier(ObjectReference src, Address slot,
+                                 double value, Word metaDataA, Word metaDataB, int mode) {
+    VM.barriers.performWriteInBarrier(src, slot, value, metaDataA, metaDataB, mode);
+  }
+
+  /**
+   * A float needs to be written into an object
+   * @param src The object into which the new primitive will be stored
+   * @param slot The address into which the new primitive will be stored.
+   * @param value The new float
+   * @param metaDataA A value that assists the host VM in creating a store
+   * @param metaDataB A value that assists the host VM in creating a store
+   * @param mode The mode of the store (eg putfield, putstatic etc)
+   */
+  @Inline
+  public final void writeBarrier(ObjectReference src, Address slot,
+                                 float value, Word metaDataA, Word metaDataB, int mode) {
+    VM.barriers.performWriteInBarrier(src, slot, value, metaDataA, metaDataB, mode);
+  }
+
+  /**
+   * An integer needs to be written into an object
+   * @param src The object into which the new primitive will be stored
+   * @param slot The address into which the new primitive will be stored.
+   * @param value The new int
+   * @param metaDataA A value that assists the host VM in creating a store
+   * @param metaDataB A value that assists the host VM in creating a store
+   * @param mode The mode of the store (eg putfield, putstatic etc)
+   */
+  @Inline
+  public final void writeBarrier(ObjectReference src, Address slot,
+                                 int value, Word metaDataA, Word metaDataB, int mode) {
+    VM.barriers.performWriteInBarrier(src, slot, value, metaDataA, metaDataB, mode);
+  }
+
+  /**
+   * A long needs to be written into an object
+   * @param src The object into which the new primitive will be stored
+   * @param slot The address into which the new primitive will be stored.
+   * @param value The new long
+   * @param metaDataA A value that assists the host VM in creating a store
+   * @param metaDataB A value that assists the host VM in creating a store
+   * @param mode The mode of the store (eg putfield, putstatic etc)
+   */
+  @Inline
+  public final void writeBarrier(ObjectReference src, Address slot,
+                                 long value, Word metaDataA, Word metaDataB, int mode) {
+    VM.barriers.performWriteInBarrier(src, slot, value, metaDataA, metaDataB, mode);
+  }
+
+  /**
+   * A short needs to be written into an object
+   * @param src The object into which the new primitive will be stored
+   * @param slot The address into which the new primitive will be stored.
+   * @param value The new short
+   * @param metaDataA A value that assists the host VM in creating a store
+   * @param metaDataB A value that assists the host VM in creating a store
+   * @param mode The mode of the store (eg putfield, putstatic etc)
+   */
+  @Inline
+  public final void writeBarrier(ObjectReference src, Address slot,
+                                 short value, Word metaDataA, Word metaDataB, int mode) {
+    VM.barriers.performWriteInBarrier(src, slot, value, metaDataA, metaDataB, mode);
+  }
+
+  /**
+   * A unboxed {@link Word} needs to be written into an object
+   * @param src The object into which the new Word will be stored
+   * @param slot The address into which the new Word will be stored.
+   * @param value The new word
+   * @param metaDataA A value that assists the host VM in creating a store
+   * @param metaDataB A value that assists the host VM in creating a store
+   * @param mode The mode of the store (eg putfield, putstatic etc)
+   */
+  @Inline
+  public final void writeBarrier(ObjectReference src, Address slot,
+                                 Word value, Word metaDataA, Word metaDataB, int mode) {
+    VM.barriers.performRawWriteInBarrier(src, slot, value, metaDataA, metaDataB, mode);
+  }
+}
diff --git a/build/configs/ExtremeAssertionsBaseBaseUsePrimitiveWriteBarriers.properties b/build/configs/ExtremeAssertionsBaseBaseUsePrimitiveWriteBarriers.properties
new file mode 100644
index 0000000..fb949ba
--- /dev/null
+++ b/build/configs/ExtremeAssertionsBaseBaseUsePrimitiveWriteBarriers.properties
@@ -0,0 +1,14 @@
+#
+#  This file is part of the Jikes RVM project (http://jikesrvm.org).
+#
+#  This file is licensed to You under the Eclipse Public License (EPL);
+#  You may not use this file except in compliance with the License. You
+#  may obtain a copy of the License at
+#
+#      http://www.opensource.org/licenses/eclipse-1.0.php
+#
+#  See the COPYRIGHT.txt file distributed with this work for information
+#  regarding copyright ownership.
+#
+config.mmtk.plan=org.mmtk.plan.semispace.usePrimitiveWriteBarriers.UsePrimitiveWriteBarriers
+config.assertions=extreme
diff --git a/build/configs/ExtremeAssertionsOptAdaptiveUsePrimitiveWriteBarriers.properties b/build/configs/ExtremeAssertionsOptAdaptiveUsePrimitiveWriteBarriers.properties
new file mode 100644
index 0000000..5abedd9
--- /dev/null
+++ b/build/configs/ExtremeAssertionsOptAdaptiveUsePrimitiveWriteBarriers.properties
@@ -0,0 +1,18 @@
+#
+#  This file is part of the Jikes RVM project (http://jikesrvm.org).
+#
+#  This file is licensed to You under the Eclipse Public License (EPL);
+#  You may not use this file except in compliance with the License. You
+#  may obtain a copy of the License at
+#
+#      http://www.opensource.org/licenses/eclipse-1.0.php
+#
+#  See the COPYRIGHT.txt file distributed with this work for information
+#  regarding copyright ownership.
+#
+config.mmtk.plan=org.mmtk.plan.semispace.usePrimitiveWriteBarriers.UsePrimitiveWriteBarriers
+config.assertions=extreme
+config.include.aos=true
+config.runtime.compiler=opt
+config.bootimage.compiler=opt
+config.bootimage.compiler.args=-X:bc:O2