added a new ToString method to Word, DWord, and QWord classes.

The ToString method will concatenate the string representations of the high and low words (or dwords) to create a single string representation of the entire word.
This can be used to more easily write and read the value from the MC and CU classes.

Models.cs

@@ -133,11 +133,24 @@ namespace CPUSimulation
             return addressString;
         }
     }
+
+
+    /// <summary>
+    /// A word is a collection of 2 Bytes
+    /// </summary>
     public class Word
     {
         Byte[] _bytes;
         public Word(Byte[] bytes)
         {
+            if (bytes.Length == 0 || bytes.Length > 2)
+            {
+                throw new ArgumentException("A word must consist of 1 or 2 bytes.");
+            }
+            else if (bytes.Length == 1)
+            {
+                _bytes = new Byte[2] { new Byte("00000000"), bytes[0] };
+            }
             _bytes = bytes;
         }
 
@@ -164,4 +177,42 @@ namespace CPUSimulation
             return wordString;
         }
     }
+
+    /// <summary>
+    /// A double word is a collection of 2 Words, or 4 Bytes
+    /// </summary>
+    public class DWord
+    {
+        Word _highWord;
+        Word _lowWord;
+        public DWord(Word highWord, Word lowWord)
+        {
+            _highWord = highWord;
+            _lowWord = lowWord;
+        }
+
+        public override string ToString()
+        {
+            return _highWord.ToString() + _lowWord.ToString();
+        }
+    }
+
+    /// <summary>
+    /// A quad word is a collection of 2 Double Words, or 8 Bytes
+    /// </summary>
+    public class QWord
+    {
+        DWord _highDWord;
+        DWord _lowDWord;
+        public QWord(DWord highDWord, DWord lowDWord)
+        {
+            _highDWord = highDWord;
+            _lowDWord = lowDWord;
+        }
+
+        override public string ToString()
+        {
+            return _highDWord.ToString() + _lowDWord.ToString();
+        }
+    }
 }