diff --git a/PDP11/pdp11_defs.h b/PDP11/pdp11_defs.h
index 6c70a70c..71e40f53 100644
--- a/PDP11/pdp11_defs.h
+++ b/PDP11/pdp11_defs.h
@@ -483,8 +483,7 @@ typedef struct {
 
 /* IO parameters */
 
-#define DZ_MUXES        4                               /* max # of DZ muxes */
-#define DZ_LINES        8                               /* lines per DZ mux */
+#define DZ_MUXES        4                               /* default # of DZ muxes */
 #define VH_MUXES        4                               /* max # of VH muxes */
 #define DLX_LINES       16                              /* max # of KL11/DL11's */
 #define DCX_LINES       16                              /* max # of DC11's */
diff --git a/PDP11/pdp11_dz.c b/PDP11/pdp11_dz.c
index 0a4fae3f..3c5f7f61 100644
--- a/PDP11/pdp11_dz.c
+++ b/PDP11/pdp11_dz.c
@@ -78,10 +78,8 @@
 #if !defined (DZ_MUXES)
 #define DZ_MUXES        1
 #endif
-#if !defined (DZ_LINES)
-#define DZ_LINES        8
-#endif
 #define MAX_DZ_MUXES    32
+#define DZ_LINES        (UNIBUS ? 8 : 4)                /* lines per DZ mux */
 
 #if DZ_MUXES > MAX_DZ_MUXES
 #error "Too many DZ multiplexers"
@@ -234,7 +232,7 @@ uint32 dz_txi = 0;                                      /* xmt interrupts */
 int32 dz_mctl = 0;                                      /* modem ctrl enabled */
 int32 dz_auto = 0;                                      /* autodiscon enabled */
 TMLN *dz_ldsc = NULL;                                   /* line descriptors */
-TMXR dz_desc = { DZ_MUXES * DZ_LINES, 0, 0, NULL };     /* mux descriptor */
+TMXR dz_desc = { 0, 0, 0, NULL };                       /* mux descriptor */
 
 /* debugging bitmaps */
 #define DBG_REG  0x0001                                 /* trace read/write registers */
@@ -277,6 +275,7 @@ void dz_clr_rxint (int32 dz);
 void dz_set_rxint (int32 dz);
 void dz_clr_txint (int32 dz);
 void dz_set_txint (int32 dz);
+t_stat dz_show_vec (FILE *st, UNIT *uptr, int32 val, CONST void *desc);
 t_stat dz_setnl (UNIT *uptr, int32 val, CONST char *cptr, void *desc);
 t_stat dz_set_log (UNIT *uptr, int32 val, CONST char *cptr, void *desc);
 t_stat dz_set_nolog (UNIT *uptr, int32 val, CONST char *cptr, void *desc);
@@ -337,8 +336,8 @@ MTAB dz_mod[] = {
         NULL, &tmxr_show_cstat, (void *) &dz_desc, "Display multiplexer statistics" },
     { MTAB_XTD|MTAB_VDV|MTAB_VALR, 010, "ADDRESS", "ADDRESS",
         &set_addr, &show_addr, NULL, "Bus address" },
-    { MTAB_XTD|MTAB_VDV|MTAB_VALR, DZ_LINES, "VECTOR", "VECTOR",
-        &set_vec, &show_vec_mux, (void *) &dz_desc, "Interrupt vector" },
+    { MTAB_XTD|MTAB_VDV|MTAB_VALR, 0, "VECTOR", "VECTOR",
+        &set_vec, &dz_show_vec, (void *) &dz_desc, "Interrupt vector" },
 #if !defined (VM_PDP10)
     { MTAB_XTD|MTAB_VDV, 0, NULL, "AUTOCONFIGURE",
         &set_addr_flt, NULL, NULL, "Enable autoconfiguration of address & vector" },
@@ -780,16 +779,26 @@ int32 i, ndev;
 
 sim_debug(DBG_TRC, dptr, "dz_reset()\n");
 
-if (dz_ldsc == NULL)
+if (dz_ldsc == NULL) {
+    dz_desc.lines = DZ_MUXES * DZ_LINES;
     dz_desc.ldsc = dz_ldsc = (TMLN *)calloc (dz_desc.lines, sizeof(*dz_ldsc));
+    }
+if ((dz_desc.lines % DZ_LINES) != 0) {      /* Transition from Qbus to Unibus device */
+    int32 newln = DZ_LINES * (1 + (dz_desc.lines / DZ_LINES));
+
+    dz_desc.ldsc = dz_ldsc = (TMLN *)realloc(dz_ldsc, newln*sizeof(*dz_ldsc));
+    memset (dz_ldsc + dz_desc.lines, 0, sizeof(*dz_ldsc)*(newln-dz_desc.lines));
+    dz_desc.lines = newln;
+    }
 tmxr_set_port_speed_control (&dz_desc);
 for (i = 0; i < dz_desc.lines/DZ_LINES; i++)            /* init muxes */
     dz_clear (i, TRUE);
 dz_rxi = dz_txi = 0;                                    /* clr master int */
 CLR_INT (DZRX);
 CLR_INT (DZTX);
-sim_cancel (dz_unit);                                  /* stop poll */
+sim_cancel (dz_unit);                                   /* stop poll */
 ndev = ((dptr->flags & DEV_DIS)? 0: (dz_desc.lines / DZ_LINES));
+dz_dib.lnt = ndev * IOLN_DZ;                            /* set length */
 return auto_config (dptr->name, ndev);                  /* auto config */
 }
 
@@ -843,6 +852,14 @@ tmxr_clear_modem_control_passthru (&dz_desc);
 return r;
 }
 
+t_stat dz_show_vec (FILE *st, UNIT *uptr, int32 arg, CONST void *desc)
+{
+const TMXR *mp = (const TMXR *) desc;
+
+return show_vec (st, uptr, ((mp->lines * 2) / DZ_LINES), desc);
+}
+
+
 /* SET LINES processor */
 
 t_stat dz_setnl (UNIT *uptr, int32 val, CONST char *cptr, void *desc)
diff --git a/VAX/vax610_defs.h b/VAX/vax610_defs.h
index e5a7da17..57bc805b 100644
--- a/VAX/vax610_defs.h
+++ b/VAX/vax610_defs.h
@@ -169,8 +169,7 @@ extern t_stat cpu_show_memory (FILE* st, UNIT* uptr, int32 val, CONST void* desc
 
 /* I/O system definitions */
 
-#define DZ_MUXES        4                               /* max # of DZV muxes */
-#define DZ_LINES        4                               /* lines per DZV mux */
+#define DZ_MUXES        4                               /* default # of DZV muxes */
 #define VH_MUXES        4                               /* max # of DHQ muxes */
 #define MT_MAXFR        (1 << 16)                       /* magtape max rec */
 
diff --git a/VAX/vax630_defs.h b/VAX/vax630_defs.h
index 59d5f5f3..fd5f1a89 100644
--- a/VAX/vax630_defs.h
+++ b/VAX/vax630_defs.h
@@ -219,8 +219,7 @@ extern t_stat cpu_show_memory (FILE* st, UNIT* uptr, int32 val, CONST void* desc
 
 /* I/O system definitions */
 
-#define DZ_MUXES        4                               /* max # of DZV muxes */
-#define DZ_LINES        4                               /* lines per DZV mux */
+#define DZ_MUXES        4                               /* default # of DZV muxes */
 #define VH_MUXES        4                               /* max # of DHQ muxes */
 #define MT_MAXFR        (1 << 16)                       /* magtape max rec */
 
diff --git a/VAX/vax730_defs.h b/VAX/vax730_defs.h
index c863ede4..1ed11411 100644
--- a/VAX/vax730_defs.h
+++ b/VAX/vax730_defs.h
@@ -204,8 +204,7 @@ extern t_stat cpu_show_memory (FILE* st, UNIT* uptr, int32 val, CONST void* desc
 
 /* I/O system definitions */
 
-#define DZ_MUXES        4                               /* max # of DZV muxes */
-#define DZ_LINES        8                               /* lines per DZV mux */
+#define DZ_MUXES        4                               /* default # of DZV muxes */
 #define VH_MUXES        4                               /* max # of DHQ muxes */
 #define DLX_LINES       16                              /* max # of KL11/DL11's */
 #define DCX_LINES       16                              /* max # of DC11's */
diff --git a/VAX/vax750_defs.h b/VAX/vax750_defs.h
index a534410e..4e5007b8 100644
--- a/VAX/vax750_defs.h
+++ b/VAX/vax750_defs.h
@@ -236,8 +236,7 @@ extern t_stat vax750_show_bootdev (FILE *st, UNIT *uptr, int32 val, CONST void *
 
 /* I/O system definitions */
 
-#define DZ_MUXES        4                               /* max # of DZV muxes */
-#define DZ_LINES        8                               /* lines per DZV mux */
+#define DZ_MUXES        4                               /* default # of DZV muxes */
 #define VH_MUXES        4                               /* max # of DHQ muxes */
 #define DLX_LINES       16                              /* max # of KL11/DL11's */
 #define DCX_LINES       16                              /* max # of DC11's */
diff --git a/VAX/vax780_defs.h b/VAX/vax780_defs.h
index bbbbf452..94ac0f79 100644
--- a/VAX/vax780_defs.h
+++ b/VAX/vax780_defs.h
@@ -253,8 +253,7 @@ extern t_stat cpu_show_memory (FILE* st, UNIT* uptr, int32 val, CONST void* desc
 
 /* I/O system definitions */
 
-#define DZ_MUXES        4                               /* max # of DZV muxes */
-#define DZ_LINES        8                               /* lines per DZV mux */
+#define DZ_MUXES        4                               /* default # of DZV muxes */
 #define VH_MUXES        4                               /* max # of DHU muxes */
 #define DLX_LINES       16                              /* max # of KL11/DL11's */
 #define DCX_LINES       16                              /* max # of DC11's */
diff --git a/VAX/vax860_defs.h b/VAX/vax860_defs.h
index c281f38b..be403fda 100644
--- a/VAX/vax860_defs.h
+++ b/VAX/vax860_defs.h
@@ -282,8 +282,7 @@ extern t_stat cpu_show_memory (FILE* st, UNIT* uptr, int32 val, CONST void* desc
 
 /* I/O system definitions */
 
-#define DZ_MUXES        4                               /* max # of DZV muxes */
-#define DZ_LINES        8                               /* lines per DZV mux */
+#define DZ_MUXES        4                               /* default # of DZV muxes */
 #define VH_MUXES        4                               /* max # of DHU muxes */
 #define DLX_LINES       16                              /* max # of KL11/DL11's */
 #define DCX_LINES       16                              /* max # of DC11's */
diff --git a/VAX/vaxmod_defs.h b/VAX/vaxmod_defs.h
index 5bd7ec9c..1e064942 100644
--- a/VAX/vaxmod_defs.h
+++ b/VAX/vaxmod_defs.h
@@ -271,8 +271,7 @@ extern t_stat cpu_show_memory (FILE* st, UNIT* uptr, int32 val, CONST void* desc
 
 /* I/O system definitions */
 
-#define DZ_MUXES        4                               /* max # of DZV muxes */
-#define DZ_LINES        4                               /* lines per DZV mux */
+#define DZ_MUXES        4                               /* default # of DZV muxes */
 #define VH_MUXES        4                               /* max # of DHQ muxes */
 #define MT_MAXFR        (1 << 16)                       /* magtape max rec */