diff --git a/ChangeLog b/ChangeLog
index f2e1d0e45..a6ae35bbd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -3,7 +3,32 @@
 	* Headers/gnustep/base/NSGString.h:
 	* Headers/gnustep/base/NSGCString.h:
 	* Source/NSGString.m:
-	* Source/NSGCString.m: Removed classes - no loinger used.
+	* Source/NSGCString.m: Removed classes - no longer used.
+	* Headers/gnustep/base/NSObjCRuntime.h:
+	* Headers/gnustep/base/fast.x:
+	* Source/GSString.m:
+	* Source/Makefile.postamble:
+	* Source/NSArchiver.m:
+	* Source/NSCTemplateValue.m:
+	* Source/NSConcreteValue.m:
+	* Source/NSCountedSet.m:
+	* Source/NSDate.m:
+	* Source/NSDictionary.m:
+	* Source/NSDistantObject.m:
+	* Source/NSGSet.m:
+	* Source/NSNumber.m:
+	* Source/NSObject.m:
+	* Source/NSScanner.m:
+	* Source/NSSerializer.m:
+	* Source/NSSet.m:
+	* Source/NSUnarchiver.m:
+	Changed calls to 'fastClass()' to use 'GSObjCClassOfObject()' and
+	added that to NSObjCRuntime.h.  Removed central class and
+	implementation caching from NSObject.m and fast.x since it was not
+	being effectively used.  New intention to do removal of fast.x and
+	add similar functionality to NSObjCRuntime.h - intention being to
+	combine functionality of fast access to the runtime, and hiding both
+	GNU and Apple runtime behind a single interface.
 
 2000-10-30  Richard Frith-Macdonald <rfm@gnu.org>
 
diff --git a/Headers/gnustep/base/NSObjCRuntime.h b/Headers/gnustep/base/NSObjCRuntime.h
index eaf51cce8..50bacd24b 100644
--- a/Headers/gnustep/base/NSObjCRuntime.h
+++ b/Headers/gnustep/base/NSObjCRuntime.h
@@ -1,5 +1,5 @@
 /* Interface to ObjC runtime for GNUStep
-   Copyright (C) 1995, 1997 Free Software Foundation, Inc.
+   Copyright (C) 1995, 1997, 2000 Free Software Foundation, Inc.
 
    Written by:  Andrew Kachites McCallum <mccallum@gnu.ai.mit.edu>
    Date: 1995
@@ -38,21 +38,22 @@
 
 @class	NSString;
 
-GS_EXPORT NSString *NSStringFromSelector(SEL aSelector);
-GS_EXPORT SEL NSSelectorFromString(NSString *aSelectorName);
-GS_EXPORT Class NSClassFromString(NSString *aClassName);
-GS_EXPORT NSString *NSStringFromClass(Class aClass);
-GS_EXPORT const char *NSGetSizeAndAlignment(const char *typePtr, unsigned int *sizep, unsigned int *alignp);
+GS_EXPORT NSString	*NSStringFromSelector(SEL aSelector);
+GS_EXPORT SEL		NSSelectorFromString(NSString *aSelectorName);
+GS_EXPORT Class		NSClassFromString(NSString *aClassName);
+GS_EXPORT NSString	*NSStringFromClass(Class aClass);
+GS_EXPORT const char	*NSGetSizeAndAlignment(const char *typePtr,
+  unsigned int *sizep, unsigned int *alignp);
 
 /* Logging */
 /* OpenStep spec states that log messages go to stderr, but just in case
    someone wants them to go somewhere else, they can implement a function
    like this */
 typedef void NSLog_printf_handler (NSString* message);
-GS_EXPORT NSLog_printf_handler *_NSLog_printf_handler;
+GS_EXPORT NSLog_printf_handler	*_NSLog_printf_handler;
 
-GS_EXPORT void NSLog (NSString* format, ...);
-GS_EXPORT void NSLogv (NSString* format, va_list args);
+GS_EXPORT void			NSLog (NSString* format, ...);
+GS_EXPORT void			NSLogv (NSString* format, va_list args);
 
 #ifndef YES
 #define YES		1
@@ -64,12 +65,23 @@ GS_EXPORT void NSLogv (NSString* format, va_list args);
 #define nil		0
 #endif nil
 
-#ifndef	NO_GNUSTEP
-GS_EXPORT BOOL GSGetInstanceVariable(id obj, NSString *name, void* data);
-GS_EXPORT BOOL GSSetInstanceVariable(id obj, NSString *name, const void* data);
-#endif
-
 #define FOUNDATION_EXPORT
 #define FOUNDATION_STATIC_INLINE static inline
 
+#ifndef	NO_GNUSTEP
+GS_EXPORT BOOL GSGetInstanceVariable(id obj, NSString *name, void* data);
+GS_EXPORT BOOL GSSetInstanceVariable(id obj, NSString *name, const void* data);
+
+/*
+ * GSObjCClassOfInstance() return the class of an instance.
+ * The argument to this function must NOT be nil.
+ */
+FOUNDATION_STATIC_INLINE Class
+GSObjCClassOfObject(id obj)
+{
+  return obj->class_pointer;
+}
+
+#endif
+
 #endif /* __NSObjCRuntime_h_GNUSTEP_BASE_INCLUDE */
diff --git a/Headers/gnustep/base/fast.x b/Headers/gnustep/base/fast.x
index ad3495a0f..c21a9be7d 100644
--- a/Headers/gnustep/base/fast.x
+++ b/Headers/gnustep/base/fast.x
@@ -36,61 +36,15 @@
  *	This file is all to do with improving performance by avoiding the
  *	Objective-C messaging overhead in time-critical code.
  *
- *	The motiviation behind it is to keep all the information needed to
- *	do that in one place (using a single mechanism), so that optimization 
- *	attempts can be kept track of.
+ *	THIS STUFF IS GOING AWAY!
  *
- *	The optimisations are of three sorts -
- *
- *	1.  inline functions
- *	    There are many operations that can be speeded up by using inline
- *	    code to examine objects rather than sending messages to them to
- *	    ask them about themselves.  Often, the objc runtime provides
- *	    functions to do this, but these sometimes perform unnecessary
- *	    checks.  Here we attempt to provide some basics.
- *
- *	2.  class comparison
- *	    It is often necessary to check the class of objects - instead of
- *	    using [+class] method, we can cache certain classes in a global
- *	    structure (The [NSObject +initialize] method does the caching)
- *	    and refer to the structure elements directly.
- *
- *	3.  direct method despatch
- *	    A common techique is to obtain the method implementation for a
- *	    specific message sent to a particular class of object, and call
- *	    the implementation directly to avoid repeated lookup within the
- *	    objc runtime.
- *	    While there is no huge speed advantage to caching the method
- *	    implementations, it does make it easy to search the source for
- *	    code that is using this technique and referring to a cached
- *	    method implementation.
+ *	The intention is to provide similar functionality in NSObjCRuntime.h
+ *	There will be GNUstep specific (mostly inline) functions added to
+ *	the header to provide direct access to runtime functinality and the
+ *	internals of objects.  Hopefully a simple configuration option will
+ *	let us build for either the GNU or the Apple runtime.
  */
 
-/*
- *	Structure to cache class information.
- *	By convention, the name of the structure element is the name of the
- *	class with an underscore prepended.
- */
-typedef struct {
-    Class	_NSArray;
-    Class	_NSMutableArray;
-    Class	_NSDictionary;
-    Class	_NSMutableDictionary;
-    Class	_NSDataMalloc;
-    Class	_NSMutableDataMalloc;
-} fastCls;
-GS_EXPORT fastCls	_fastCls;	/* Populated by _fastBuildCache()	*/
-
-/*
- *	The '_fastBuildCache()' function is called to populate the cache
- *	structures.  This is (at present) called in [NSObject +initialize]
- *	but you may call it explicitly later to repopulate the cache after
- *	changes have been made to the runtime by loading of categories or
- *	by classes posing as other classes.
- */
-GS_EXPORT void	_fastBuildCache();
-
-
 /*
  *	The '_fastMallocBuffer()' function is called to get a chunk of
  *	memory that will automatically be released when the current
@@ -100,9 +54,6 @@ GS_EXPORT void	*_fastMallocBuffer(unsigned size);
 
 /*
  *	Fast access to class info - DON'T pass nil to these!
- *	These should really do different things conditional upon the objc
- *	runtime in use, but we will probably only ever want to support the
- *	latest GNU runtime, so I haven't bothered about that.
  */
 
 static INLINE BOOL
diff --git a/Source/GSString.m b/Source/GSString.m
index 2c2994766..67a7d0f4d 100644
--- a/Source/GSString.m
+++ b/Source/GSString.m
@@ -43,6 +43,7 @@
 #include <Foundation/NSRange.h>
 #include <Foundation/NSException.h>
 #include <Foundation/NSValue.h>
+#include <Foundation/NSObjCRuntime.h>
 #include <base/behavior.h>
 /* memcpy(), strlen(), strcmp() are gcc builtin's */
 
@@ -359,7 +360,7 @@ compare_c(ivars self, NSString *aString, unsigned mask, NSRange aRange)
   if (fastIsInstance(aString) == NO)
     return strCompCsNs((id)self, aString, mask, aRange);
 
-  c = fastClass(aString);
+  c = GSObjCClassOfObject(aString);
   if (fastClassIsKindOfClass(c, GSUStringClass) == YES
     || (c == GSMStringClass && ((ivars)aString)->_flags.wide == 1))
     return strCompCsUs((id)self, aString, mask, aRange);
@@ -381,7 +382,7 @@ compare_u(ivars self, NSString *aString, unsigned mask, NSRange aRange)
   if (fastIsInstance(aString) == NO)
     return strCompUsNs((id)self, aString, mask, aRange);
 
-  c = fastClass(aString);
+  c = GSObjCClassOfObject(aString);
   if (fastClassIsKindOfClass(c, GSUStringClass)
     || (c == GSMStringClass && ((ivars)aString)->_flags.wide == 1))
     return strCompUsUs((id)self, aString, mask, aRange);
@@ -1057,7 +1058,7 @@ rangeOfString_c(ivars self, NSString *aString, unsigned mask, NSRange aRange)
   if (fastIsInstance(aString) == NO)
     return strRangeCsNs((id)self, aString, mask, aRange);
 
-  c = fastClass(aString);
+  c = GSObjCClassOfObject(aString);
   if (fastClassIsKindOfClass(c, GSUStringClass) == YES
     || (c == GSMStringClass && ((ivars)aString)->_flags.wide == 1))
     return strRangeCsUs((id)self, aString, mask, aRange);
@@ -1079,7 +1080,7 @@ rangeOfString_u(ivars self, NSString *aString, unsigned mask, NSRange aRange)
   if (fastIsInstance(aString) == NO)
     return strRangeUsNs((id)self, aString, mask, aRange);
 
-  c = fastClass(aString);
+  c = GSObjCClassOfObject(aString);
   if (fastClassIsKindOfClass(c, GSUStringClass) == YES
     || (c == GSMStringClass && ((ivars)aString)->_flags.wide == 1))
     return strRangeUsUs((id)self, aString, mask, aRange);
@@ -1137,7 +1138,7 @@ transmute(ivars self, NSString *aString)
 {
   ivars	other;
   BOOL	transmute;
-  Class	c = fastClass(aString);
+  Class	c = GSObjCClassOfObject(aString);	// NB aString must not be nil
 
   other = (ivars)aString;
   transmute = YES;
@@ -2202,6 +2203,12 @@ transmute(ivars self, NSString *aString)
   unsigned	length;
 
   GS_RANGE_CHECK(aRange, _count);
+  if (aString == nil)
+    [NSException raise: NSInvalidArgumentException
+		format: @"replace characters with nil string"];
+  if (fastIsInstance(aString) == NO)
+    [NSException raise: NSInvalidArgumentException
+		format: @"replace characters with non-string"];
 
   length = (aString == nil) ? 0 : [aString length];
   offset = length - aRange.length;
diff --git a/Source/Makefile.postamble b/Source/Makefile.postamble
index d66ca973d..c3ee4df1b 100644
--- a/Source/Makefile.postamble
+++ b/Source/Makefile.postamble
@@ -244,6 +244,22 @@ $(GNUSTEP_OBJ_DIR)/NSString.o \
 $(GNUSTEP_OBJ_DIR)/NSUnarchiver.o \
         : $(HEADER_DIR)/fast.x
 
+#
+#	Files that include NSObjCRuntime.h will need a rebuild if it is changed.
+#
+$(GNUSTEP_OBJ_DIR)/GSString.o \
+$(GNUSTEP_OBJ_DIR)/NSArchiver.o \
+$(GNUSTEP_OBJ_DIR)/NSArray.o \
+$(GNUSTEP_OBJ_DIR)/NSData.o \
+$(GNUSTEP_OBJ_DIR)/NSGDictionary.o \
+$(GNUSTEP_OBJ_DIR)/NSInvocation.o \
+$(GNUSTEP_OBJ_DIR)/NSObjCRuntime.o \
+$(GNUSTEP_OBJ_DIR)/NSObject.o \
+$(GNUSTEP_OBJ_DIR)/NSSerializer.o \
+$(GNUSTEP_OBJ_DIR)/NSString.o \
+$(GNUSTEP_OBJ_DIR)/NSUnarchiver.o \
+        : $(HEADER_DIR)/NSObjCRuntime.h
+
 #
 #	Files that include GSeq.h will need a rebuild if it is changed.
 #
diff --git a/Source/NSArchiver.m b/Source/NSArchiver.m
index 57fb15385..054aa8134 100644
--- a/Source/NSArchiver.m
+++ b/Source/NSArchiver.m
@@ -60,6 +60,9 @@ static SEL xRefSel;
 static SEL eObjSel;
 static SEL eValSel;
 
+@class NSMutableDataMalloc;
+static Class	NSMutableDataMallocClass;
+
 + (void) initialize
 {
   if (self == [NSArchiver class])
@@ -69,6 +72,7 @@ static SEL eValSel;
       xRefSel = @selector(serializeTypeTag:andCrossRef:);
       eObjSel = @selector(encodeObject:);
       eValSel = @selector(encodeValueOfObjCType:at:);
+      NSMutableDataMallocClass = [NSMutableDataMalloc class];
     }
 }
 
@@ -76,7 +80,7 @@ static SEL eValSel;
 {
   NSMutableData	*d;
 
-  d = [[_fastCls._NSMutableDataMalloc allocWithZone: fastZone(self)] init];
+  d = [[NSMutableDataMallocClass allocWithZone: fastZone(self)] init];
   self = [self initForWritingWithMutableData: d];
   RELEASE(d);
   return self;
@@ -162,7 +166,7 @@ static SEL eValSel;
   id		d;
   NSZone	*z = NSDefaultMallocZone();
 
-  d = [[_fastCls._NSMutableDataMalloc allocWithZone: z] initWithCapacity: 0];
+  d = [[NSMutableDataMallocClass allocWithZone: z] initWithCapacity: 0];
   if (d == nil)
     {
       return nil;
diff --git a/Source/NSCTemplateValue.m b/Source/NSCTemplateValue.m
index d374613ac..e0bc3d56e 100644
--- a/Source/NSCTemplateValue.m
+++ b/Source/NSCTemplateValue.m
@@ -27,6 +27,7 @@
 #include <Foundation/NSString.h>
 #include <Foundation/NSException.h>
 #include <Foundation/NSCoder.h>
+#include <Foundation/NSObjCRuntime.h>
 #include <base/preface.h>
 #include <base/fast.x>
 
@@ -81,7 +82,8 @@
 
 - (BOOL) isEqual: (id)other
 {
-  if (other != nil && fastInstanceIsKindOfClass(other, fastClass(self)))
+  if (other != nil
+    && fastInstanceIsKindOfClass(other, GSObjCClassOfObject(self)))
     {
       return [self isEqualToValue: other];
     }
@@ -92,7 +94,8 @@
 {
   typedef __typeof__(data) _dt;
 
-  if (aValue != nil && fastInstanceIsKindOfClass(aValue, fastClass(self)))
+  if (aValue != nil
+    && fastInstanceIsKindOfClass(aValue, GSObjCClassOfObject(self)))
     {
       _dt	val = [aValue TYPE_METHOD];
 #if TYPE_ORDER == 0
diff --git a/Source/NSConcreteValue.m b/Source/NSConcreteValue.m
index f6b9a6a0a..9b94f4972 100644
--- a/Source/NSConcreteValue.m
+++ b/Source/NSConcreteValue.m
@@ -28,6 +28,7 @@
 #include <Foundation/NSException.h>
 #include <Foundation/NSCoder.h>
 #include <Foundation/NSZone.h>
+#include <Foundation/NSObjCRuntime.h>
 #include <base/preface.h>
 #include <base/fast.x>
 
@@ -104,7 +105,7 @@
 
 - (BOOL) isEqualToValue: (NSValue*)aValue
 {
-  if (fastClass(aValue) != fastClass(self))
+  if (GSObjCClassOfObject(aValue) != GSObjCClassOfObject(self))
     return NO;
   if (strcmp(objctype, ((NSConcreteValue*)aValue)->objctype) != 0)
     return NO;
diff --git a/Source/NSCountedSet.m b/Source/NSCountedSet.m
index 31a098c3f..5a11c0ae4 100644
--- a/Source/NSCountedSet.m
+++ b/Source/NSCountedSet.m
@@ -33,6 +33,7 @@
 #include <Foundation/NSLock.h>
 #include <Foundation/NSNotification.h>
 #include <Foundation/NSThread.h>
+#include <Foundation/NSObjCRuntime.h>
 
 @class	NSSetNonCore;
 @class	NSMutableSetNonCore;
@@ -110,7 +111,7 @@ static Class NSCountedSet_concrete_class;
 - (id) initWithCoder: (NSCoder*)aCoder
 {
   unsigned	count;
-  Class		c = fastClass(self);
+  Class		c = GSObjCClassOfObject(self);
 
   if (c == NSCountedSet_abstract_class)
     {
diff --git a/Source/NSDate.m b/Source/NSDate.m
index b9fd6de32..8a8a0a2c4 100644
--- a/Source/NSDate.m
+++ b/Source/NSDate.m
@@ -33,6 +33,7 @@
 #include <Foundation/NSUserDefaults.h>
 #include <Foundation/NSCharacterSet.h>
 #include <Foundation/NSScanner.h>
+#include <Foundation/NSObjCRuntime.h>
 #include <base/preface.h>
 #include <base/behavior.h>
 #include <base/fast.x>
@@ -97,8 +98,13 @@ findInArray(NSArray *array, unsigned pos, NSString *str)
 static inline NSTimeInterval
 otherTime(NSDate* other)
 {
-  Class	c = fastClass(other);
+  Class	c;
 
+  if (other == nil)
+    [NSException raise: NSInvalidArgumentException format: @"other time nil"];
+  if (fastIsInstance(other) == NO)
+    [NSException raise: NSInvalidArgumentException format: @"other time bad"];
+  c = GSObjCClassOfObject(other);
   if (c == concreteClass || c == calendarClass)
     return ((NSGDate*)other)->_seconds_since_ref;
   else
diff --git a/Source/NSDictionary.m b/Source/NSDictionary.m
index f3f680b2d..a392f40da 100644
--- a/Source/NSDictionary.m
+++ b/Source/NSDictionary.m
@@ -35,6 +35,7 @@
 #include <Foundation/NSUserDefaults.h>
 #include <Foundation/NSCoder.h>
 #include <Foundation/NSDebug.h>
+#include <Foundation/NSObjCRuntime.h>
 
 @interface NSDictionaryNonCore : NSDictionary
 @end
@@ -779,14 +780,14 @@ static NSString	*indentStrings[] = {
 
       for (i = 0; i < numKeys; i++)
 	{
-	  if (fastClass(keys[i]) == lastClass)
+	  if (GSObjCClassOfObject(keys[i]) == lastClass)
 	    continue;
 	  if ([keys[i] respondsToSelector: @selector(compare:)] == NO)
 	    {
 	      canCompare = NO;
 	      break;
 	    }
-	  lastClass = fastClass(keys[i]);
+	  lastClass = GSObjCClassOfObject(keys[i]);
 	}
 
       if (canCompare == YES)
@@ -830,7 +831,7 @@ static NSString	*indentStrings[] = {
 		      Class			x;
 		      NSComparisonResult	r;
 
-		      x = fastClass(a);
+		      x = GSObjCClassOfObject(a);
 		      if (x != lastClass)
 			{
 			  lastClass = x;
diff --git a/Source/NSDistantObject.m b/Source/NSDistantObject.m
index 2896092a1..a4e2dc10e 100644
--- a/Source/NSDistantObject.m
+++ b/Source/NSDistantObject.m
@@ -30,6 +30,7 @@
 #include <Foundation/NSPort.h>
 #include <Foundation/NSMethodSignature.h>
 #include <Foundation/NSException.h>
+#include <Foundation/NSObjCRuntime.h>
 
 static int	debug_proxy = 0;
 static Class	placeHolder = 0;
@@ -742,7 +743,7 @@ enum
 
 - (IMP) methodForSelector: (SEL)aSelector
 {
-  return get_imp(fastClass((id)self), aSelector);
+  return get_imp(GSObjCClassOfObject((id)self), aSelector);
 }
 
 - (NSMethodSignature*) methodSignatureForSelector: (SEL)aSelector
diff --git a/Source/NSGSet.m b/Source/NSGSet.m
index 0905e084b..fef35c095 100644
--- a/Source/NSGSet.m
+++ b/Source/NSGSet.m
@@ -33,6 +33,7 @@
 #include <Foundation/NSString.h>
 #include <Foundation/NSPortCoder.h>
 #include <Foundation/NSDebug.h>
+#include <Foundation/NSObjCRuntime.h>
 
 #define	GSI_MAP_HAS_VALUE	0
 #define	GSI_MAP_KTYPES		GSUNION_OBJ
@@ -249,7 +250,7 @@ static Class	mutableSetClass;
     return NO;
 
   // Loop for all members in otherSet
-  c = fastClass(otherSet);
+  c = GSObjCClassOfObject(otherSet);
   if (c == setClass || c == mutableSetClass)
     {
       GSIMapNode	node = ((NSGSet*)otherSet)->map.firstNode;
@@ -319,7 +320,7 @@ static Class	mutableSetClass;
     }
   else
     {
-      Class	c = fastClass(other);
+      Class	c = GSObjCClassOfObject(other);
 
       if (c == setClass || c == mutableSetClass)
 	{
diff --git a/Source/NSNumber.m b/Source/NSNumber.m
index ef94815ae..c9004c542 100644
--- a/Source/NSNumber.m
+++ b/Source/NSNumber.m
@@ -36,6 +36,7 @@
 #include <Foundation/NSThread.h>
 #include <Foundation/NSCoder.h>
 #include <Foundation/NSPortCoder.h>
+#include <Foundation/NSObjCRuntime.h>
 
 @implementation NSNumber
 
@@ -56,7 +57,9 @@ GSNumberInfoFromObject(NSNumber *o)
   Class		c;
   GSNumberInfo	*info;
 
-  c = fastClass(o);
+  if (o == nil)
+    return nil;
+  c = GSObjCClassOfObject(o);
   info = (GSNumberInfo*)NSMapGet (numberMap, (void*)c);
   if (info == 0)
     {
@@ -664,7 +667,7 @@ static Class	doubleNumberClass;
 
 - (NSString*) descriptionWithLocale: (NSDictionary*)locale
 {
-  if (fastClass(self) == abstractClass)
+  if (GSObjCClassOfObject(self) == abstractClass)
     {
       [NSException raise: NSInternalInconsistencyException
 		  format: @"descriptionWithLocale: for abstract NSNumber"];
@@ -725,7 +728,7 @@ static Class	doubleNumberClass;
 /* All the rest of these methods must be implemented by a subclass */
 - (BOOL) boolValue
 {
-  if (fastClass(self) == abstractClass)
+  if (GSObjCClassOfObject(self) == abstractClass)
     [NSException raise: NSInternalInconsistencyException
 		format: @"get boolValue from abstract NSNumber"];
   else
@@ -835,7 +838,7 @@ static Class	doubleNumberClass;
 
 - (signed char) charValue
 {
-  if (fastClass(self) == abstractClass)
+  if (GSObjCClassOfObject(self) == abstractClass)
     [NSException raise: NSInternalInconsistencyException
 		format: @"get charValue from abstract NSNumber"];
   else
@@ -945,7 +948,7 @@ static Class	doubleNumberClass;
 
 - (double) doubleValue
 {
-  if (fastClass(self) == abstractClass)
+  if (GSObjCClassOfObject(self) == abstractClass)
     [NSException raise: NSInternalInconsistencyException
 		format: @"get doubleValue from abstract NSNumber"];
   else
@@ -1055,7 +1058,7 @@ static Class	doubleNumberClass;
 
 - (float) floatValue
 {
-  if (fastClass(self) == abstractClass)
+  if (GSObjCClassOfObject(self) == abstractClass)
     [NSException raise: NSInternalInconsistencyException
 		format: @"get floatValue from abstract NSNumber"];
   else
@@ -1165,7 +1168,7 @@ static Class	doubleNumberClass;
 
 - (signed int) intValue
 {
-  if (fastClass(self) == abstractClass)
+  if (GSObjCClassOfObject(self) == abstractClass)
     [NSException raise: NSInternalInconsistencyException
 		format: @"get intValue from abstract NSNumber"];
   else
@@ -1275,7 +1278,7 @@ static Class	doubleNumberClass;
 
 - (signed long long) longLongValue
 {
-  if (fastClass(self) == abstractClass)
+  if (GSObjCClassOfObject(self) == abstractClass)
     [NSException raise: NSInternalInconsistencyException
 		format: @"get longLongValue from abstract NSNumber"];
   else
@@ -1385,7 +1388,7 @@ static Class	doubleNumberClass;
 
 - (signed long) longValue
 {
-  if (fastClass(self) == abstractClass)
+  if (GSObjCClassOfObject(self) == abstractClass)
     [NSException raise: NSInternalInconsistencyException
 		format: @"get longValue from abstract NSNumber"];
   else
@@ -1495,7 +1498,7 @@ static Class	doubleNumberClass;
 
 - (signed short) shortValue
 {
-  if (fastClass(self) == abstractClass)
+  if (GSObjCClassOfObject(self) == abstractClass)
     [NSException raise: NSInternalInconsistencyException
 		format: @"get shortValue from abstract NSNumber"];
   else
@@ -1610,7 +1613,7 @@ static Class	doubleNumberClass;
 
 - (unsigned char) unsignedCharValue
 {
-  if (fastClass(self) == abstractClass)
+  if (GSObjCClassOfObject(self) == abstractClass)
     [NSException raise: NSInternalInconsistencyException
 		format: @"get unsignedCharrValue from abstract NSNumber"];
   else
@@ -1720,7 +1723,7 @@ static Class	doubleNumberClass;
 
 - (unsigned int) unsignedIntValue
 {
-  if (fastClass(self) == abstractClass)
+  if (GSObjCClassOfObject(self) == abstractClass)
     [NSException raise: NSInternalInconsistencyException
 		format: @"get unsignedIntValue from abstract NSNumber"];
   else
@@ -1830,7 +1833,7 @@ static Class	doubleNumberClass;
 
 - (unsigned long long) unsignedLongLongValue
 {
-  if (fastClass(self) == abstractClass)
+  if (GSObjCClassOfObject(self) == abstractClass)
     [NSException raise: NSInternalInconsistencyException
 		format: @"get unsignedLongLongValue from abstract NSNumber"];
   else
@@ -1940,7 +1943,7 @@ static Class	doubleNumberClass;
 
 - (unsigned long) unsignedLongValue
 {
-  if (fastClass(self) == abstractClass)
+  if (GSObjCClassOfObject(self) == abstractClass)
     [NSException raise: NSInternalInconsistencyException
 		format: @"get unsignedLongValue from abstract NSNumber"];
   else
@@ -2050,7 +2053,7 @@ static Class	doubleNumberClass;
 
 - (unsigned short) unsignedShortValue
 {
-  if (fastClass(self) == abstractClass)
+  if (GSObjCClassOfObject(self) == abstractClass)
     [NSException raise: NSInternalInconsistencyException
 		format: @"get unsignedShortValue from abstract NSNumber"];
   else
diff --git a/Source/NSObject.m b/Source/NSObject.m
index 123d572b7..eaf4999a4 100644
--- a/Source/NSObject.m
+++ b/Source/NSObject.m
@@ -40,14 +40,13 @@
 #include <Foundation/NSDebug.h>
 #include <Foundation/NSThread.h>
 #include <Foundation/NSNotification.h>
+#include <Foundation/NSObjCRuntime.h>
 #include <limits.h>
 
 #include <base/fast.x>
 
 extern BOOL __objc_responds_to(id, SEL);
 
-fastCls	_fastCls;	/* Structure to cache classes.	*/
-
 @class	_FastMallocBuffer;
 static Class	fastMallocClass;
 static unsigned	fastMallocOffset;
@@ -57,20 +56,6 @@ static Class	NXConstantStringClass;
 @class	NSDataMalloc;
 @class	NSMutableDataMalloc;
 
-void	_fastBuildCache()
-{
-  /*
-   *	Cache some classes for quick access later.
-   */
-
-  _fastCls._NSArray = [NSArray class];
-  _fastCls._NSMutableArray = [NSMutableArray class];
-  _fastCls._NSDictionary = [NSDictionary class];
-  _fastCls._NSMutableDictionary = [NSMutableDictionary class];
-  _fastCls._NSDataMalloc = [NSDataMalloc class];
-  _fastCls._NSMutableDataMalloc = [NSMutableDataMalloc class];
-}
-
 
 /*
  *	Reference count and memory management
@@ -424,7 +409,7 @@ NSDeallocateObject(NSObject *anObject)
 inline NSZone *
 fastZone(NSObject *object)
 {
-  if (fastClass(object) == NXConstantStringClass)
+  if (GSObjCClassOfObject(object) == NXConstantStringClass)
     return NSDefaultMallocZone();
   return ((obj)object)[-1].zone;
 }
@@ -434,7 +419,7 @@ fastZone(NSObject *object)
 inline NSZone *
 fastZone(NSObject *object)
 {
-  if (fastClass(object) == NXConstantStringClass)
+  if (GSObjCClassOfObject(object) == NXConstantStringClass)
     return NSDefaultMallocZone();
   return NSZoneFromPointer(&((obj)object)[-1]);
 }
@@ -495,7 +480,7 @@ NSDeallocateObject(NSObject *anObject)
 inline NSZone *
 fastZone(NSObject *object)
 {
-  if (fastClass(object) == NXConstantStringClass)
+  if (GSObjCClassOfObject(object) == NXConstantStringClass)
     return NSDefaultMallocZone();
   return NSZoneFromPointer(object);
 }
@@ -622,7 +607,6 @@ static BOOL double_release_check_enabled = NO;
       fastMallocOffset = 0;
 #endif
       NXConstantStringClass = [NXConstantString class];
-      _fastBuildCache();
       GSBuildStrings();
       [[NSNotificationCenter defaultCenter]
 	addObserver: self
@@ -754,12 +738,12 @@ static BOOL deallocNotifications = NO;
 - (IMP) methodForSelector: (SEL)aSelector
 {
   /*
-   *	If 'self' is an instance, fastClass() will get the class,
+   *	If 'self' is an instance, GSObjCClassOfObject() will get the class,
    *	and get_imp() will get the instance method.
-   *	If 'self' is a class, fastClass() will get the meta-class,
+   *	If 'self' is a class, GSObjCClassOfObject() will get the meta-class,
    *	and get_imp() will get the class method.
    */
-  return get_imp(fastClass(self), aSelector);
+  return get_imp(GSObjCClassOfObject(self), aSelector);
 }
 
 + (NSMethodSignature*) instanceMethodSignatureForSelector: (SEL)aSelector
@@ -843,7 +827,6 @@ static BOOL deallocNotifications = NO;
    *	We may have replaced a class in the cache, or may have replaced one
    *	which had cached methods, so we must rebuild the cache.
    */
-  _fastBuildCache();
 }
 
 - (void) doesNotRecognizeSelector: (SEL)aSelector
@@ -911,7 +894,7 @@ static BOOL deallocNotifications = NO;
        * use get_imp() because NSDistantObject doesn't implement
        * methodForSelector:
        */
-      proxyImp = get_imp(fastClass((id)proxyClass),
+      proxyImp = get_imp(GSObjCClassOfObject((id)proxyClass),
 	@selector(proxyWithLocal:connection:));
     }
 
@@ -1025,7 +1008,7 @@ static BOOL deallocNotifications = NO;
       return nil;
     }
     
-  msg = get_imp(fastClass(self), aSelector);
+  msg = get_imp(GSObjCClassOfObject(self), aSelector);
   if (!msg)
     {
       [NSException raise: NSGenericException
@@ -1046,7 +1029,7 @@ static BOOL deallocNotifications = NO;
       return nil;
     }
     
-  msg = get_imp(fastClass(self), aSelector);
+  msg = get_imp(GSObjCClassOfObject(self), aSelector);
   if (!msg)
     {
       [NSException raise: NSGenericException
@@ -1070,7 +1053,7 @@ static BOOL deallocNotifications = NO;
       return nil;
     }
   
-  msg = get_imp(fastClass(self), aSelector);
+  msg = get_imp(GSObjCClassOfObject(self), aSelector);
   if (!msg)
     {
       [NSException raise: NSGenericException
@@ -1113,9 +1096,9 @@ static BOOL deallocNotifications = NO;
 {
 #if 0
   if (fastIsInstance(self))
-    return (class_get_instance_method(fastClass(self), aSelector)!=METHOD_NULL);
+    return (class_get_instance_method(GSObjCClassOfObject(self), aSelector)!=METHOD_NULL);
   else
-    return (class_get_class_method(fastClass(self), aSelector)!=METHOD_NULL);
+    return (class_get_class_method(GSObjCClassOfObject(self), aSelector)!=METHOD_NULL);
 #else
   return __objc_responds_to(self, aSelector);
 #endif
diff --git a/Source/NSScanner.m b/Source/NSScanner.m
index 016be0d07..cb24dc991 100644
--- a/Source/NSScanner.m
+++ b/Source/NSScanner.m
@@ -27,6 +27,7 @@
 #include <Foundation/NSScanner.h>
 #include <Foundation/NSException.h>
 #include <Foundation/NSUserDefaults.h>
+#include <Foundation/NSObjCRuntime.h>
 #include <float.h>
 #include <limits.h>
 #include <math.h>
@@ -126,7 +127,7 @@ typedef struct {
       aString = @"";
     }
 
-  c = fastClass(aString);
+  c = GSObjCClassOfObject(aString);
   if (c == GSUString_class)
     {
       _isUnicode = YES;
diff --git a/Source/NSSerializer.m b/Source/NSSerializer.m
index 35aca19c5..98b70a226 100644
--- a/Source/NSSerializer.m
+++ b/Source/NSSerializer.m
@@ -34,6 +34,7 @@
 #include <Foundation/NSSet.h>
 #include <Foundation/NSThread.h>
 #include <Foundation/NSNotificationQueue.h>
+#include <Foundation/NSObjCRuntime.h>
 
 #include <base/NSGArray.h>
 
@@ -133,8 +134,9 @@ static SEL	setSel;
 static void
 initSerializerInfo(_NSSerializerInfo* info, NSMutableData *d, BOOL u)
 {
-  Class	c = fastClass(d);
+  Class	c;
 
+  c = GSObjCClassOfObject(d);
   info->data = d; 
   info->appImp = (void (*)())get_imp(c, appSel);
   info->datImp = (void* (*)())get_imp(c, datSel);
@@ -160,8 +162,9 @@ endSerializerInfo(_NSSerializerInfo* info)
 static void
 serializeToInfo(id object, _NSSerializerInfo* info)
 {
-  Class	c = fastClass(object);
+  Class	c;
 
+  c = GSObjCClassOfObject(object);
   if (fastIsClass(c) == NO)
     {
       [NSException raise: NSInvalidArgumentException
diff --git a/Source/NSSet.m b/Source/NSSet.m
index 2f5244f72..4b52bed3d 100644
--- a/Source/NSSet.m
+++ b/Source/NSSet.m
@@ -31,6 +31,7 @@
 #include <Foundation/NSUtilities.h>
 #include <Foundation/NSString.h>
 #include <Foundation/NSException.h>
+#include <Foundation/NSObjCRuntime.h>
 
 @interface NSSetNonCore : NSSet
 @end
@@ -120,8 +121,9 @@ static Class NSMutableSet_concrete_class;
 - (id) initWithCoder: (NSCoder*)aCoder
 {
   unsigned	count;
-  Class		c = fastClass(self);
+  Class		c;
 
+  c = GSObjCClassOfObject(self);
   if (c == NSSet_abstract_class)
     {
       RELEASE(self);
diff --git a/Source/NSUnarchiver.m b/Source/NSUnarchiver.m
index 1f6a75e92..4ad28c9cb 100644
--- a/Source/NSUnarchiver.m
+++ b/Source/NSUnarchiver.m
@@ -27,6 +27,7 @@
 #include <Foundation/NSZone.h>
 #include <Foundation/NSException.h>
 #include <Foundation/NSByteOrder.h>
+#include <Foundation/NSObjCRuntime.h>
 
 /*
  *	Setup for inline operation of arrays.
@@ -294,6 +295,9 @@ mapClassName(NSUnarchiverObjectInfo *info)
 
 @implementation NSUnarchiver
 
+@class NSDataMalloc;
+static Class NSDataMallocClass;
+
 + (void) initialize
 {
   if ([self class] == [NSUnarchiver class])
@@ -302,6 +306,7 @@ mapClassName(NSUnarchiverObjectInfo *info)
       tagSel = @selector(deserializeTypeTag:andCrossRef:atCursor:);
       dValSel = @selector(decodeValueOfObjCType:at:);
       clsDict = [[NSMutableDictionary alloc] initWithCapacity: 200];
+      NSDataMallocClass = [NSDataMalloc class];
     }
 }
 
@@ -328,7 +333,7 @@ mapClassName(NSUnarchiverObjectInfo *info)
 
 + (id) unarchiveObjectWithFile: (NSString*)path
 {
-  NSData	*d = [_fastCls._NSDataMalloc dataWithContentsOfFile: path];
+  NSData	*d = [NSDataMallocClass dataWithContentsOfFile: path];
 
   if (d != nil)
     {
@@ -1144,7 +1149,7 @@ mapClassName(NSUnarchiverObjectInfo *info)
 
       TEST_RELEASE(data);
       data = RETAIN(anObject);
-      c = fastClass(data);
+      c = GSObjCClassOfObject(data);
       if (src != self)
 	{
 	  src = data;