diff --git a/Ample/Slot.h b/Ample/Slot.h
index 952b6c7..6302136 100644
--- a/Ample/Slot.h
+++ b/Ample/Slot.h
@@ -10,6 +10,17 @@
 #import <Cocoa/Cocoa.h>
 #import "Media.h"
 
+/* number of slot types.  bitmask used so should be < sizeof(unsigned *8) */
+#define SLOT_COUNT 23
+static_assert(SLOT_COUNT <= sizeof(unsigned) * 8, "too many slot types");
+
+#define kSMARTPORT_SLOT 21
+#define kBIOS_SLOT 22
+
+#ifndef SIZEOF
+#define SIZEOF(x) (sizeof(x) / sizeof(x[0]))
+#endif
+
 //NS_ASSUME_NONNULL_BEGIN
 @class Slot, SlotOption, SlotTableCellView;
 
diff --git a/Ample/Slot.m b/Ample/Slot.m
index 835698f..89daef4 100644
--- a/Ample/Slot.m
+++ b/Ample/Slot.m
@@ -101,9 +101,10 @@ static NSDictionary *IndexMap = nil;
         @"nbe":        @20,
 
         @"smartport":  @21,
-#define kSMARTPORT 21
+        @"bios":       @22,
     };
-    
+    static_assert(kSMARTPORT_SLOT == 21, "Smartport != 21");
+    static_assert(kBIOS_SLOT == 22, "Bios != 22");
 }
 
 -(void)reset {
@@ -156,7 +157,7 @@ static NSDictionary *IndexMap = nil;
     // { 'sl3' : 'uthernet' }
 
     // special case for smartport since the name isn't used.
-    if (_index == kSMARTPORT) {
+    if (_index == kSMARTPORT_SLOT) {
         SlotOption *option = [_options objectAtIndex: _selectedIndex];
         [option reserialize: dict];
         return;
@@ -387,7 +388,7 @@ static NSDictionary *IndexMap = nil;
 
     // [menu setItemArray: ] doesn't work prior to 10.14, apparently.
     [menu removeAllItems];
-    if (_index == kSMARTPORT) {
+    if (_index == kSMARTPORT_SLOT) {
         //[menu setItemArray: @[]];
         [button setHidden: YES];
     } else {
diff --git a/Ample/SlotViewController.m b/Ample/SlotViewController.m
index f6550db..1573069 100644
--- a/Ample/SlotViewController.m
+++ b/Ample/SlotViewController.m
@@ -16,11 +16,7 @@
 
 #import <objc/runtime.h>
 
-/* number of slot types.  bitmask used so should be < sizeof(unsigned *8) */
-#define SLOT_COUNT 22
-static_assert(SLOT_COUNT <= sizeof(unsigned) * 8, "too many slot types");
 
-#define SIZEOF(x) (sizeof(x) / sizeof(x[0]))
 
 
 static unsigned RootKey = 0;
@@ -120,6 +116,7 @@ static unsigned RootKey = 0;
         _slot_object[i] = nil;
     }
     
+    _slot_value[kBIOS_SLOT] = nil; // don't copy over to other machines.
 
     extern NSArray *BuildSlots(NSString *name, NSDictionary *data);
     _root = BuildSlots(_machine, d);