diff --git a/mps/src/thlii4.c b/mps/src/thlii4.c
new file mode 100644
index 00000000000..9b0251f9a3b
--- /dev/null
+++ b/mps/src/thlii4.c
@@ -0,0 +1,279 @@
+/*  impl.c.thlii3: Threads Manager for Intel x86 systems with LinuxThreads
+ *
+ *  $HopeName: $
+ *  Copyright (C) 2000 Harlequin Ltd, all rights reserved
+ *
+ *  This is a pthreads implementation of the threads manager.
+ *  See design.mps.thread-manager.
+ *
+ *  This supports the impl.h.th
+ *
+ * .thread.id: The thread id is used to identify the current thread.
+ *
+ * ASSUMPTIONS
+ *
+ * .error.resume: PThreadextResume is assumed to succeed unless the thread
+ * has been destroyed.
+ * .error.suspend: PThreadextSuspend is assumed to succeed unless the thread
+ * has been destroyed. In this case, the suspend context is set to NULL;
+ *
+ * .stack.full-descend:  assumes full descending stack.
+ * i.e. stack pointer points to the last allocated location;
+ * stack grows downwards.
+ *
+ * .stack.below-bottom: it's legal for the stack pointer to be at a 
+ * higher address than the registered bottom of stack. This might 
+ * happen if the stack of another thread doesn't contain any frames 
+ * belonging to the client language. In this case, the stack should
+ * not be scanned.
+ *
+ * .stack.align: assume roots on the stack are always word-aligned,
+ * but don't assume that the stack pointer is necessarily 
+ * word-aligned at the time of reading the context of another thread.
+ *
+ * .i3: assumes MPS_ARCH_I3
+ * .i3.sp: The sp in the context is Esp
+ * .context.regroots: the root regs are Edi, Esi, Ebx, Edx, Ecx, Eax are
+ * assumed to be recorded in the context at pointer-aligned boundaries
+ */
+
+#include "prmcli.h"
+#include "mpm.h"
+
+#if !defined(MPS_OS_LI) || !defined(MPS_ARCH_I3) 
+#error "Compiling thlii3 when MPS_OS_LI or MPS_ARCH_I3 not defined."
+#endif
+
+#include <pthread.h>
+#include "pthrdext.h"
+
+SRCID(thlii3, "$HopeName: $");
+
+
+typedef struct ThreadStruct {    /* PThreads thread structure */
+  Sig sig;                       /* design.mps.sig */
+  Serial serial;                 /* from arena->threadSerial */
+  Arena arena;                   /* owning arena */
+  RingStruct arenaRing;          /* threads attached to arena */
+  PThreadextStruct thrextStruct; /* PThreads extension */
+  pthread_t id;                  /* Pthread object of thread */
+  struct sigcontext *scpSusp;    /* Context if thread is suspended */
+} ThreadStruct;
+
+
+Bool ThreadCheck(Thread thread)
+{
+  CHECKS(Thread, thread);
+  CHECKU(Arena, thread->arena);
+  CHECKL(thread->serial < thread->arena->threadSerial);
+  CHECKL(RingCheck(&thread->arenaRing));
+  CHECKD(PThreadext, &thread->thrextStruct);
+  return TRUE;
+}
+
+Bool ThreadCheckSimple(Thread thread)
+{
+  CHECKS(Thread, thread);
+  return TRUE;
+}
+
+
+Res ThreadRegister(Thread *threadReturn, Arena arena)
+{
+  Res res;
+  Thread thread;
+  void *p;
+
+  AVER(threadReturn != NULL);
+  AVERT(Arena, arena);
+
+  res = ControlAlloc(&p, arena, sizeof(ThreadStruct), 
+                     /* withReservoirPermit */ FALSE);
+  if(res != ResOK) 
+    return res;
+  thread = (Thread)p;
+
+  thread->id = pthread_self();
+
+  RingInit(&thread->arenaRing);
+
+  thread->sig = ThreadSig;
+  thread->serial = arena->threadSerial;
+  ++arena->threadSerial;
+  thread->arena = arena;
+  thread->scpSusp = NULL;
+
+  PThreadextInit(&thread->thrextStruct, thread->id);
+
+  AVERT(Thread, thread);
+
+  RingAppend(ArenaThreadRing(arena), &thread->arenaRing);
+
+  *threadReturn = thread;
+  return ResOK;
+}
+
+
+void ThreadDeregister(Thread thread, Arena arena)
+{
+  AVERT(Thread, thread);
+  AVERT(Arena, arena);
+
+  RingRemove(&thread->arenaRing);
+
+  thread->sig = SigInvalid;
+
+  RingFinish(&thread->arenaRing);
+
+  PThreadextFinish(&thread->thrextStruct);
+
+  ControlFree(arena, thread, sizeof(ThreadStruct));
+}
+
+
+/*  Map over threads on ring calling f on each one except the
+ *  current thread.
+ */
+
+static void mapThreadRing(Ring threadRing, void (*func)(Thread))
+{
+  Ring node, next;
+  pthread_t self;
+
+  AVERT(Ring, threadRing);
+
+  self = pthread_self();
+  RING_FOR(node, threadRing, next) {
+    Thread thread = RING_ELT(Thread, arenaRing, node);
+    AVERT(Thread, thread);
+    if(! pthread_equal(self, thread->id)) /* .thread.id */
+      (*func)(thread);
+  }
+}
+
+static void threadSuspend(Thread thread)
+{
+  /* .error.suspend */
+  /* In the error case (PThreadextSuspend returning ResFAIL), we */
+  /* assume the thread has been destroyed. */
+  /* In which case we simply continue. */
+  Res res;
+  res = PThreadextSuspend(&thread->thrextStruct, &thread->scpSusp);
+  if(res != ResOK)
+    thread->scpSusp = NULL;
+}
+
+void ThreadRingSuspend(Ring threadRing)
+{
+  mapThreadRing(threadRing, threadSuspend);
+}
+
+static void threadResume(Thread thread)
+{
+  /* .error.resume */
+  /* If the previous suspend failed (thread->scpSusp == NULL), */
+  /* or in the error case (PThreadextResume returning ResFAIL), */
+  /* assume the thread has been destroyed. */
+  /* In which case we simply continue. */
+  if(thread->scpSusp != NULL) {
+    (void)PThreadextResume(&thread->thrextStruct);
+    thread->scpSusp = NULL;
+  }
+}
+
+void ThreadRingResume(Ring threadRing)
+{
+  mapThreadRing(threadRing, threadResume);
+}
+
+
+Thread ThreadRingThread(Ring threadRing)
+{
+  Thread thread;
+  AVERT(Ring, threadRing);
+  thread = RING_ELT(Thread, arenaRing, threadRing);
+  AVERT(Thread, thread);
+  return thread;
+}
+
+
+/* Must be thread-safe.  See design.mps.interface.c.thread-safety. */
+Arena ThreadArena(Thread thread)
+{
+  /* Can't AVER thread as that would not be thread-safe */
+  /* AVERT(Thread, thread); */
+  return thread->arena;
+}
+
+
+Res ThreadScan(ScanState ss, Thread thread, void *stackBot)
+{
+  pthread_t self;
+  Res res;
+
+  AVERT(Thread, thread);
+  self = pthread_self();
+  if(pthread_equal(self, thread->id)) {
+    /* scan this thread's stack */
+    res = StackScan(ss, stackBot);
+    if(res != ResOK)
+      return res;
+  } else {
+    struct sigcontext *scp;
+    Addr *stackBase, *stackLimit, stackPtr;
+
+    scp = thread->scpSusp;
+    if(scp == NULL) {
+      /* .error.suspend */
+      /* We assume that the thread must have been destroyed. */
+      /* We ignore the situation by returning immediately. */
+      return ResOK;
+    }
+
+    stackPtr  = (Addr)scp->esp;   /* .i3.sp */
+    /* .stack.align */
+    stackBase  = (Addr *)AddrAlignUp(stackPtr, sizeof(Addr));
+    stackLimit = (Addr *)stackBot;
+    if (stackBase >= stackLimit)
+      return ResOK;    /* .stack.below-bottom */
+
+    /* scan stack inclusive of current sp and exclusive of
+     * stackBot (.stack.full-descend)
+     */
+    res = TraceScanAreaTagged(ss, stackBase, stackLimit);
+    if(res != ResOK)
+      return res;
+
+    /* (.context.regroots)
+     * This scans the root registers (.context.regroots).  It also
+     * unecessarily scans the rest of the context.  The optimisation
+     * to scan only relevent parts would be machine dependent.
+     */
+    res = TraceScanAreaTagged(ss, (Addr *)scp,
+           (Addr *)((char *)scp + sizeof(*scp)));
+    if(res != ResOK)
+      return res;
+  }
+
+  return ResOK;
+}
+
+
+Res ThreadDescribe(Thread thread, mps_lib_FILE *stream)
+{
+  Res res;
+  
+  res = WriteF(stream,
+               "Thread $P ($U) {\n", (WriteFP)thread, (WriteFU)thread->serial,
+               "  arena $P ($U)\n",  
+               (WriteFP)thread->arena, (WriteFU)thread->arena->serial,
+               "  id $U\n",          (WriteFU)thread->id,
+               "} Thread $P ($U)\n", (WriteFP)thread, (WriteFU)thread->serial,
+               NULL);
+  if(res != ResOK) 
+    return res;
+
+  return ResOK;
+}
+
+