diff --git a/imlac/DisplayProcessor.cs b/imlac/DisplayProcessor.cs
index 3904fc1..77130e0 100644
--- a/imlac/DisplayProcessor.cs
+++ b/imlac/DisplayProcessor.cs
@@ -45,8 +45,8 @@ namespace imlac
         {
             _system = system;
             _mem = _system.Memory;
-            _instructionCache = new DisplayInstruction[Memory.Size];
             _dtStack = new Stack<ushort>(8);
+            InitializeCache();
         }
 
         public void Reset()
@@ -156,6 +156,11 @@ namespace imlac
             get { return _dpcEntry; }
         }
 
+        public void InitializeCache()
+        {
+            _instructionCache = new DisplayInstruction[Memory.Size];
+        }
+
         public void InvalidateCache(ushort address)
         {
             _instructionCache[address & Memory.SizeMask] = null;
diff --git a/imlac/IO/TTY.cs b/imlac/IO/TTY.cs
index 51f12f0..9792bd3 100644
--- a/imlac/IO/TTY.cs
+++ b/imlac/IO/TTY.cs
@@ -166,7 +166,7 @@ namespace imlac.IO
         private byte _txData;
 
         private int _clocks;
-        private readonly int _dataClocks = 100;
+        private readonly int _dataClocks = 250;
 
         private ISerialDataChannel _dataChannel;
 
diff --git a/imlac/Memory.cs b/imlac/Memory.cs
index f694642..6e3b572 100644
--- a/imlac/Memory.cs
+++ b/imlac/Memory.cs
@@ -15,15 +15,39 @@
     along with sImlac.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+using System;
+
 namespace imlac
 {
-    // TODO: make memory size configurable.
     public class Memory
     {
         public Memory(ImlacSystem system)
-        {
-            _mem = new ushort[Size];
+        {            
             _system = system;
+            SetMemorySize(0x2000);
+        }
+
+        public void SetMemorySize(ushort size)
+        {
+            if (size != 0x1000 && size != 0x2000 && size != 0x4000)
+            {
+                throw new InvalidOperationException("Size must be 4k, 8k, or 16k.");
+            }
+
+            _size = size;
+            _sizeMask = (ushort)(size - 1);
+
+            _mem = new ushort[Size];
+
+            if (_system.Processor != null)
+            {
+                _system.Processor.InitializeCache();
+            }
+
+            if (_system.DisplayProcessor != null)
+            {
+                _system.DisplayProcessor.InitializeCache();
+            }
         }
 
         public ushort Fetch(ushort address)
@@ -44,13 +68,16 @@ namespace imlac
 
         public static ushort Size
         {
-            get { return 0x4000; }
+            get { return _size; }
         }
 
         public static ushort SizeMask
         {
-            get { return 0x3fff; }
-        }       
+            get { return _sizeMask; }
+        }
+
+        private static ushort _size;
+        private static ushort _sizeMask;
 
         private ushort[] _mem;
         private ImlacSystem _system;
diff --git a/imlac/Processor.cs b/imlac/Processor.cs
index 44f3fdf..394b434 100644
--- a/imlac/Processor.cs
+++ b/imlac/Processor.cs
@@ -43,11 +43,11 @@ namespace imlac
         {
             _system = system;
             _mem = _system.Memory;
-            _instructionCache = new Instruction[Memory.Size];            
 
             _iotDispatch = new IIOTDevice[0x200];   // 9 bits of IOT instructions
 
             Reset();
+            InitializeCache();
         }
 
         public void Reset()
@@ -119,6 +119,11 @@ namespace imlac
             return GetCachedInstruction(address).Disassemble(address);
         }
 
+        public void InitializeCache()
+        {
+            _instructionCache = new Instruction[Memory.Size];
+        }
+
         public void InvalidateCache(ushort address)
         {
             _instructionCache[address & Memory.SizeMask] = null;
@@ -578,7 +583,7 @@ namespace imlac
         }
 
         private ushort GetEffectiveAddress(ushort baseAddress)
-        {
+        {            
             return (ushort)((_pc & (Memory.SizeMask & 0xf800)) | (baseAddress & 0x07ff));
         }
 
diff --git a/imlac/System.cs b/imlac/System.cs
index e4dc9ad..ca72443 100644
--- a/imlac/System.cs
+++ b/imlac/System.cs
@@ -254,6 +254,29 @@ namespace imlac
             return SystemExecutionState.Debugging;
         }
 
+        [DebuggerFunction("set memory size 4kw", "Sets memory size to 4KW")]
+        private SystemExecutionState SetMemorySize4kw()
+        {
+            _memory.SetMemorySize(0x1000);
+            return SystemExecutionState.Debugging;
+        }
+
+
+        [DebuggerFunction("set memory size 8kw", "Sets memory size to 8KW")]
+        private SystemExecutionState SetMemorySize8kw()
+        {
+            _memory.SetMemorySize(0x2000);
+            return SystemExecutionState.Debugging;
+        }
+
+
+        [DebuggerFunction("set memory size 16kw", "Sets memory size to 16KW")]
+        private SystemExecutionState SetMemorySize16kw()
+        {
+            _memory.SetMemorySize(0x4000);
+            return SystemExecutionState.Debugging;
+        }
+
         [DebuggerFunction("set logging", "Sets the logging configuration", "<loglevel>")]
         private SystemExecutionState SetLogging(LogType value)
         {