diff --git a/src/config.hpp b/src/config.hpp
index 014f013..28f8bcd 100644
--- a/src/config.hpp
+++ b/src/config.hpp
@@ -53,8 +53,8 @@ namespace CosmoTool
     Exception(const char *mess = 0)
       : msg(mess) {}
 
-    const char *getMessage() const { return msg; };
-    virtual const char *what() const throw () { return msg; };
+    const char *getMessage() const { return msg != 0 ? msg : "No message"; };
+    virtual const char *what() const throw () { return msg != 0 ? msg : "What 'what' ?"; };
 
   private:
     const char *msg;
@@ -104,6 +104,13 @@ namespace CosmoTool
     EndOfFileException(const char *mess = 0)
       : Exception(mess) {}
   };
+
+  class FilesystemFullException: public Exception
+  {
+  public:
+    FilesystemFullException(const char *mess = 0)
+      : Exception(mess) {}
+  };
 };
 
 #endif
diff --git a/src/fortran.cpp b/src/fortran.cpp
index 285d100..4ca7254 100644
--- a/src/fortran.cpp
+++ b/src/fortran.cpp
@@ -155,3 +155,168 @@ int64_t UnformattedRead::readInt64()
 
   return a.i;
 }
+
+//// UnformattedWrite
+
+UnformattedWrite::UnformattedWrite(const string& fname)
+  throw(NoSuchFileException)
+{
+  f = new ofstream(fname.c_str());
+  if (!*f)
+    throw NoSuchFileException();
+
+  swapOrdering = false;
+  cSize = Check_32bits;
+  checkPointRef = checkPointAccum = 0;
+}
+
+UnformattedWrite::UnformattedWrite(const char *fname)
+  throw(NoSuchFileException)
+{
+  f = new ofstream(fname);
+  if (!*f)
+    throw NoSuchFileException();
+  swapOrdering = false;
+  cSize = Check_32bits;
+  checkPointRef = checkPointAccum = 0;
+}
+
+
+UnformattedWrite::~UnformattedWrite()
+{
+  delete f;
+}
+
+// Todo implement primitive description
+void UnformattedWrite::setOrdering(Ordering o)
+{
+  if (o == LittleEndian)
+    {
+    }
+}
+
+void UnformattedWrite::setCheckpointSize(CheckpointSize cs)
+{
+  cSize = cs;
+}
+    
+void UnformattedWrite::beginCheckpoint()
+  throw (InvalidUnformattedAccess,FilesystemFullException)
+{
+  if (checkPointAccum != 0)
+    throw InvalidUnformattedAccess();
+  
+  checkPointRef = f->tellp();
+  if (cSize == Check_32bits)
+    writeInt32(0);
+  else
+    writeInt64(0);
+
+  checkPointAccum = 0;
+
+  if (!*f)
+    throw FilesystemFullException();
+}
+
+void UnformattedWrite::endCheckpoint()
+  throw (InvalidUnformattedAccess,FilesystemFullException)
+{
+  if (checkPointAccum == 0)
+    throw InvalidUnformattedAccess();
+
+  ostream::streampos curPos = f->tellp();
+
+  int64_t deltaPos = curPos-checkPointRef;
+
+  deltaPos -= (cSize == Check_32bits) ? 4 : 8;
+  // This is a sanity check.
+  if (checkPointAccum != deltaPos)
+    throw InvalidUnformattedAccess();
+
+  uint64_t saveAccum = checkPointAccum;
+
+  f->seekp(checkPointRef);
+  if (cSize == Check_32bits)
+    writeInt32(saveAccum);
+  else
+    writeInt64(saveAccum);
+
+  f->seekp(curPos);
+  if (cSize == Check_32bits)
+    writeInt32(saveAccum);
+  else
+    writeInt64(saveAccum);
+
+  checkPointAccum = checkPointRef = 0;
+}
+
+void UnformattedWrite::writeOrderedBuffer(void *buffer, int size)
+  throw (FilesystemFullException)
+{
+  f->write((char *)buffer, size);
+  
+  if (swapOrdering)
+    {
+      char *cb = (char *)buffer;
+      for (int i = 0; i < size/2; i++)
+	swap(cb[i], cb[size-i-1]);
+    }
+  checkPointAccum += size;
+
+  if (!*f)
+    throw FilesystemFullException();
+}
+  
+void UnformattedWrite::writeReal64(double d)
+  throw (FilesystemFullException)
+{
+  union
+  {
+    char b[8];
+    double d;
+  } a;
+
+  a.d = d;
+
+  writeOrderedBuffer(&a, 8);
+}
+
+void UnformattedWrite::writeReal32(float f)
+  throw (FilesystemFullException)
+{
+  union
+  {
+    char b[4];
+    float f;
+  } a;
+  
+  a.f = f;
+
+  writeOrderedBuffer(&a, 4);
+}
+
+void UnformattedWrite::writeInt32(int32_t i)
+  throw (FilesystemFullException)
+{
+  union
+  {
+    char b[4];
+    int32_t i;
+  } a;
+
+  a.i = i;
+  writeOrderedBuffer(&a, 4);
+}
+
+void UnformattedWrite::writeInt64(int64_t i)
+  throw (FilesystemFullException)
+{
+  union
+  {
+    char b[8];
+    int64_t i;
+  } a;
+
+  a.i = i;
+  writeOrderedBuffer(&a, 8);
+}
diff --git a/src/fortran.hpp b/src/fortran.hpp
index 361978e..6c5a52e 100644
--- a/src/fortran.hpp
+++ b/src/fortran.hpp
@@ -13,7 +13,7 @@ namespace CosmoTool
   {
   };
 
-  class UnformattedRead
+  class FortranTypes
   {
   public:
     enum Ordering {
@@ -23,6 +23,11 @@ namespace CosmoTool
     enum CheckpointSize {
       Check_32bits, Check_64bits
     };
+  };
+
+  class UnformattedRead: public FortranTypes
+  {
+  public:
 
     UnformattedRead(const std::string& fname)
       throw (NoSuchFileException);
@@ -59,6 +64,45 @@ namespace CosmoTool
       throw (InvalidUnformattedAccess);
   };
 
+ class UnformattedWrite: public FortranTypes
+  {
+  public:
+
+    UnformattedWrite(const std::string& fname)
+      throw (NoSuchFileException);
+    UnformattedWrite(const char *fname)
+      throw (NoSuchFileException);
+    ~UnformattedWrite();
+
+    // Todo implement primitive description
+    void setOrdering(Ordering o);
+    void setCheckpointSize(CheckpointSize cs);
+    
+    void beginCheckpoint()
+      throw (FilesystemFullException,InvalidUnformattedAccess);
+    void endCheckpoint()
+      throw (FilesystemFullException,InvalidUnformattedAccess);
+    
+    void writeReal64(double d)
+      throw (FilesystemFullException);
+    void writeReal32(float f)
+      throw (FilesystemFullException);
+    void writeInt32(int32_t i)
+      throw (FilesystemFullException);
+    void writeInt64(int64_t i)
+      throw (FilesystemFullException);
+
+  protected:
+    bool swapOrdering;
+    CheckpointSize cSize;
+    std::streamoff checkPointRef;
+    uint64_t checkPointAccum;
+    std::ofstream *f;
+
+    void writeOrderedBuffer(void *buffer, int size)
+      throw(FilesystemFullException);
+  };
+
 };
 
 #endif