diff --git a/mps/code/buffer.c b/mps/code/buffer.c
index 6e6616fc5b8..e55c12a7e8d 100644
--- a/mps/code/buffer.c
+++ b/mps/code/buffer.c
@@ -147,10 +147,17 @@ Bool BufferCheck(Buffer buffer)
 Res BufferDescribe(Buffer buffer, mps_lib_FILE *stream)
 {
   Res res;
+  char abzMode[5];
 
   if (!CHECKT(Buffer, buffer)) return ResFAIL;
   if (stream == NULL) return ResFAIL;
 
+  abzMode[0] = (buffer->mode & BufferModeTRANSITION)  ? 't' : '_';
+  abzMode[1] = (buffer->mode & BufferModeLOGGED)      ? 'l' : '_';
+  abzMode[2] = (buffer->mode & BufferModeFLIPPED)     ? 'f' : '_';
+  abzMode[3] = (buffer->mode & BufferModeATTACHED)    ? 'a' : '_';
+  abzMode[4] = '\0';
+
   res = WriteF(stream,
                "Buffer $P ($U) {\n",
                (WriteFP)buffer, (WriteFU)buffer->serial,
@@ -160,7 +167,8 @@ Res BufferDescribe(Buffer buffer, mps_lib_FILE *stream)
                "  Pool $P\n",        (WriteFP)buffer->pool,
                buffer->isMutator ?
                  "  Mutator Buffer\n" : "  Internal Buffer\n",
-               "  Mode $B\n",        (WriteFB)(buffer->mode),
+               "  mode $S (TRANSITION, LOGGED, FLIPPED, ATTACHED)\n",
+                       (WriteFS)abzMode,
                "  fillSize $UKb\n",  (WriteFU)(buffer->fillSize / 1024),
                "  emptySize $UKb\n", (WriteFU)(buffer->emptySize / 1024),
                "  alignment $W\n",   (WriteFW)buffer->alignment,
diff --git a/mps/code/poolamc.c b/mps/code/poolamc.c
index df0716571cb..b92e0877aca 100644
--- a/mps/code/poolamc.c
+++ b/mps/code/poolamc.c
@@ -26,6 +26,7 @@ typedef struct amcGenStruct *amcGen;
 
 /* forward declarations */
 
+static Bool amcSegHasNailboard(Seg seg);
 static Bool AMCCheck(AMC amc);
 static Res AMCFix(Pool pool, ScanState ss, Seg seg, Ref *refIO);
 static Res AMCHeaderFix(Pool pool, ScanState ss, Seg seg, Ref *refIO);
@@ -105,6 +106,9 @@ static Bool amcSegCheck(amcSeg amcseg)
   CHECKD(GCSeg, &amcseg->gcSegStruct);
   CHECKL(*amcseg->segTypeP == AMCPTypeNailboard
          || *amcseg->segTypeP == AMCPTypeGen);
+  if (*amcseg->segTypeP == AMCPTypeNailboard) {
+    CHECKL(SegNailed(amcSeg2Seg(amcseg)) != TraceSetEMPTY);
+  }
   CHECKL(BoolCheck(amcseg->new));
   return TRUE;
 }
@@ -160,7 +164,7 @@ static Res AMCSegDescribe(Seg seg, mps_lib_FILE *stream)
   if (!CHECKT(amcSeg, amcseg)) return ResFAIL;
 
   /* Describe the superclass fields first via next-method call */
-  super = SEG_SUPERCLASS(GCSegClass);
+  super = SEG_SUPERCLASS(amcSegClass);
   res = super->describe(seg, stream);
   if (res != ResOK) return res;
 
@@ -171,18 +175,33 @@ static Res AMCSegDescribe(Seg seg, mps_lib_FILE *stream)
   base = SegBase(seg);
   p = AddrAdd(base, pool->format->headerSize);
   limit = SegLimit(seg);
-  if (SegBuffer(seg) != NULL)
-    init = BufferGetInit(SegBuffer(seg));
-  else
-    init = limit;
 
   res = WriteF(stream,
                "AMC seg $P [$A,$A){\n",
                (WriteFP)seg, (WriteFA)base, (WriteFA)limit,
-               "  Map\n",
                NULL);
   if (res != ResOK) return res;
 
+  if (amcSegHasNailboard(seg)) {
+    res = WriteF(stream, "  Boarded\n", NULL);
+    /* @@@@ should have AMCNailboardDescribe() */
+  } else {
+    if (SegNailed(seg) == TraceSetEMPTY) {
+      res = WriteF(stream, "  Mobile\n", NULL);
+    } else {
+      res = WriteF(stream, "  Stuck\n", NULL);
+    }
+  }
+  if (res != ResOK) return res;
+
+  res = WriteF(stream, "  Map:  *===:object  bbbb:buffer\n", NULL);
+  if (res != ResOK) return res;
+
+  if (SegBuffer(seg) != NULL)
+    init = BufferGetInit(SegBuffer(seg));
+  else
+    init = limit;
+  
   for(i = base; i < limit; i = AddrAdd(i, row)) {
     Addr j;
     char c;
@@ -194,9 +213,9 @@ static Res AMCSegDescribe(Seg seg, mps_lib_FILE *stream)
     /* @@@@ This misses a header-sized pad at the end. */
     for(j = i; j < AddrAdd(i, row); j = AddrAdd(j, step)) {
       if (j >= limit)
-        c = ' ';
+        c = ' ';  /* if seg is not a whole number of print rows */
       else if (j >= init)
-        c = '.';
+        c = 'b';
       else if (j == p) {
         c = '*';
         p = (pool->format->skip)(p);
diff --git a/mps/code/seg.c b/mps/code/seg.c
index 05773c0198a..9acf15f73c0 100644
--- a/mps/code/seg.c
+++ b/mps/code/seg.c
@@ -1560,14 +1560,20 @@ static Res gcSegDescribe(Seg seg, mps_lib_FILE *stream)
   res = super->describe(seg, stream);
   if (res != ResOK) return res;
 
-  if (gcseg->buffer != NULL) {
-    res = BufferDescribe(gcseg->buffer, stream);
-    if (res != ResOK) return res;
-  }
   res = WriteF(stream,
                "  summary $W\n", (WriteFW)gcseg->summary,
                NULL);
-  return res;
+  if (res != ResOK) return res;
+
+  if (gcseg->buffer == NULL) {
+    res = WriteF(stream, "  buffer: NULL\n", NULL);
+  }
+  else {
+    res = BufferDescribe(gcseg->buffer, stream);
+  }
+  if (res != ResOK) return res;
+
+  return ResOK;
 }