diff --git a/src/allreduce_base.h b/src/allreduce_base.h
index bc7cc26c9..e313cab88 100644
--- a/src/allreduce_base.h
+++ b/src/allreduce_base.h
@@ -111,8 +111,8 @@ class AllreduceBase : public IEngine {
    *
    * \sa CheckPoint, VersionNumber
    */
-  virtual int LoadCheckPoint(utils::ISerializable *global_model,
-                             utils::ISerializable *local_model = NULL) {
+  virtual int LoadCheckPoint(ISerializable *global_model,
+                             ISerializable *local_model = NULL) {
     return 0;
   }
   /*!
@@ -131,8 +131,8 @@ class AllreduceBase : public IEngine {
    *
    * \sa LoadCheckPoint, VersionNumber
    */
-  virtual void CheckPoint(const utils::ISerializable *global_model,
-                          const utils::ISerializable *local_model = NULL) {
+  virtual void CheckPoint(const ISerializable *global_model,
+                          const ISerializable *local_model = NULL) {
     version_number += 1;
   }
   /*!
diff --git a/src/allreduce_robust.cc b/src/allreduce_robust.cc
index 7d339cf84..538609c62 100644
--- a/src/allreduce_robust.cc
+++ b/src/allreduce_robust.cc
@@ -11,8 +11,8 @@
 #include <utility>
 #include "./io.h"
 #include "./utils.h"
-#include "./rabit.h"
 #include "./allreduce_robust.h"
+#include "./rabit.h"
 
 namespace rabit {
 namespace engine {
@@ -141,8 +141,8 @@ void AllreduceRobust::Broadcast(void *sendrecvbuf_, size_t total_size, int root)
  *
  * \sa CheckPoint, VersionNumber
  */
-int AllreduceRobust::LoadCheckPoint(utils::ISerializable *global_model,
-                                    utils::ISerializable *local_model) {
+int AllreduceRobust::LoadCheckPoint(ISerializable *global_model,
+                                    ISerializable *local_model) {
   if (num_local_replica == 0) {
     utils::Check(local_model == NULL, "need to set num_local_replica larger than 1 to checkpoint local_model");
   }
@@ -198,8 +198,8 @@ int AllreduceRobust::LoadCheckPoint(utils::ISerializable *global_model,
  *
  * \sa LoadCheckPoint, VersionNumber
  */
-void AllreduceRobust::CheckPoint(const utils::ISerializable *global_model,
-                                 const utils::ISerializable *local_model) {
+void AllreduceRobust::CheckPoint(const ISerializable *global_model,
+                                 const ISerializable *local_model) {
   if (num_local_replica == 0) {
     utils::Check(local_model == NULL, "need to set num_local_replica larger than 1 to checkpoint local_model");
   } 
diff --git a/src/allreduce_robust.h b/src/allreduce_robust.h
index 7888a66f1..fd85e4828 100644
--- a/src/allreduce_robust.h
+++ b/src/allreduce_robust.h
@@ -75,8 +75,8 @@ class AllreduceRobust : public AllreduceBase {
    *
    * \sa CheckPoint, VersionNumber
    */
-  virtual int LoadCheckPoint(utils::ISerializable *global_model,
-                             utils::ISerializable *local_model = NULL);
+  virtual int LoadCheckPoint(ISerializable *global_model,
+                             ISerializable *local_model = NULL);
   /*!
    * \brief checkpoint the model, meaning we finished a stage of execution
    *  every time we call check point, there is a version number which will increase by one
@@ -93,8 +93,8 @@ class AllreduceRobust : public AllreduceBase {
    *
    * \sa LoadCheckPoint, VersionNumber
    */
-  virtual void CheckPoint(const utils::ISerializable *global_model,
-                          const utils::ISerializable *local_model = NULL);
+  virtual void CheckPoint(const ISerializable *global_model,
+                          const ISerializable *local_model = NULL);
   /*!
    * \brief explicitly re-init everything before calling LoadCheckPoint
    *    call this function when IEngine throw an exception out,
diff --git a/src/engine.h b/src/engine.h
index 977b0d6ff..0700b2a95 100644
--- a/src/engine.h
+++ b/src/engine.h
@@ -5,7 +5,7 @@
  */
 #ifndef RABIT_ENGINE_H
 #define RABIT_ENGINE_H
-#include "./io.h"
+#include "./serializable.h"
 
 namespace MPI {
 /*! \brief MPI data type just to be compatible with MPI reduce function*/
@@ -92,8 +92,8 @@ class IEngine {
    *
    * \sa CheckPoint, VersionNumber
    */
-  virtual int LoadCheckPoint(utils::ISerializable *global_model,
-                             utils::ISerializable *local_model = NULL) = 0;
+  virtual int LoadCheckPoint(ISerializable *global_model,
+                             ISerializable *local_model = NULL) = 0;
   /*!
    * \brief checkpoint the model, meaning we finished a stage of execution
    *  every time we call check point, there is a version number which will increase by one
@@ -110,8 +110,8 @@ class IEngine {
    *
    * \sa LoadCheckPoint, VersionNumber
    */
-  virtual void CheckPoint(const utils::ISerializable *global_model,
-                          const utils::ISerializable *local_model = NULL) = 0;
+  virtual void CheckPoint(const ISerializable *global_model,
+                          const ISerializable *local_model = NULL) = 0;
   /*!
    * \return version number of current stored model,
    *         which means how many calls to CheckPoint we made so far
diff --git a/src/engine_mpi.cc b/src/engine_mpi.cc
index 9e5972e1a..870c93fdb 100644
--- a/src/engine_mpi.cc
+++ b/src/engine_mpi.cc
@@ -34,12 +34,12 @@ class MPIEngine : public IEngine {
   virtual void InitAfterException(void) {
     utils::Error("MPI is not fault tolerant");
   }
-  virtual int LoadCheckPoint(utils::ISerializable *global_model,
-                             utils::ISerializable *local_model = NULL) {
+  virtual int LoadCheckPoint(ISerializable *global_model,
+                             ISerializable *local_model = NULL) {
     return 0;
   }
-  virtual void CheckPoint(const utils::ISerializable *global_model,
-                          const utils::ISerializable *local_model = NULL) {
+  virtual void CheckPoint(const ISerializable *global_model,
+                          const ISerializable *local_model = NULL) {
     version_number += 1;
   }
   virtual int VersionNumber(void) const {
diff --git a/src/io.h b/src/io.h
index ed01545f2..699a93c83 100644
--- a/src/io.h
+++ b/src/io.h
@@ -5,99 +5,14 @@
 #include <cstring>
 #include <string>
 #include "./utils.h"
+#include "./serializable.h"
 /*!
  * \file io.h
- * \brief general stream interface for serialization, I/O
+ * \brief utilities that implements different serializable interface
  * \author Tianqi Chen
  */
 namespace rabit {
 namespace utils {
-/*!
- * \brief interface of stream I/O, used to serialize model
- */
-class IStream {
- public:
-  /*!
-   * \brief read data from stream
-   * \param ptr pointer to memory buffer
-   * \param size size of block
-   * \return usually is the size of data readed
-   */
-  virtual size_t Read(void *ptr, size_t size) = 0;
-  /*!
-   * \brief write data to stream
-   * \param ptr pointer to memory buffer
-   * \param size size of block
-   */
-  virtual void Write(const void *ptr, size_t size) = 0;
-  /*! \brief virtual destructor */
-  virtual ~IStream(void) {}
-
- public:
-  // helper functions to write various of data structures
-  /*!
-   * \brief binary serialize a vector 
-   * \param vec vector to be serialized
-   */
-  template<typename T>
-  inline void Write(const std::vector<T> &vec) {
-    uint64_t sz = static_cast<uint64_t>(vec.size());
-    this->Write(&sz, sizeof(sz));
-    if (sz != 0) {
-      this->Write(&vec[0], sizeof(T) * sz);
-    }
-  }
-  /*!
-   * \brief binary load a vector 
-   * \param out_vec vector to be loaded
-   * \return whether load is successfull
-   */
-  template<typename T>
-  inline bool Read(std::vector<T> *out_vec) {
-    uint64_t sz;
-    if (this->Read(&sz, sizeof(sz)) == 0) return false;
-    out_vec->resize(sz);
-    if (sz != 0) {
-      if (this->Read(&(*out_vec)[0], sizeof(T) * sz) == 0) return false;
-    }
-    return true;
-  }
-  /*!
-   * \brief binary serialize a string
-   * \param str the string to be serialized
-   */ 
-  inline void Write(const std::string &str) {
-    uint64_t sz = static_cast<uint64_t>(str.length());
-    this->Write(&sz, sizeof(sz));
-    if (sz != 0) {
-      this->Write(&str[0], sizeof(char) * sz);
-    }
-  }
-  /*!
-   * \brief binary load a string
-   * \param out_str string to be loaded
-   * \return whether load is successful
-   */
-  inline bool Read(std::string *out_str) {
-    uint64_t sz;
-    if (this->Read(&sz, sizeof(sz)) == 0) return false;
-    out_str->resize(sz);
-    if (sz != 0) {
-      if (this->Read(&(*out_str)[0], sizeof(char) * sz) == 0) return false;
-    }
-    return true;
-  }
-};
-
-/*! \brief interface of se*/
-class ISerializable {
- public:
-  /*! \brief load the model from file */
-  virtual void Load(IStream &fi) = 0;
-  /*! \brief save the model to the stream*/
-  virtual void Save(IStream &fo) const = 0;
-};
-
 /*! \brief interface of i/o stream that support seek */
 class ISeekStream: public IStream {
  public:
diff --git a/src/rabit-inl.h b/src/rabit-inl.h
index 8d379f920..b6126f47d 100644
--- a/src/rabit-inl.h
+++ b/src/rabit-inl.h
@@ -6,6 +6,8 @@
  */
 #ifndef RABIT_RABIT_INL_H
 #define RABIT_RABIT_INL_H
+// use engine for implementation
+#include "./engine.h"
 
 namespace rabit {
 namespace engine {
@@ -139,13 +141,13 @@ inline void Allreduce(DType *sendrecvbuf, size_t count, std::function<void()> pr
 #endif // C++11
 
 // load latest check point
-inline int LoadCheckPoint(utils::ISerializable *global_model,
-                          utils::ISerializable *local_model) {
+inline int LoadCheckPoint(ISerializable *global_model,
+                          ISerializable *local_model) {
   return engine::GetEngine()->LoadCheckPoint(global_model, local_model);
 }
 // checkpoint the model, meaning we finished a stage of execution
-inline void CheckPoint(const utils::ISerializable *global_model,
-                       const utils::ISerializable *local_model) {
+inline void CheckPoint(const ISerializable *global_model,
+                       const ISerializable *local_model) {
   engine::GetEngine()->CheckPoint(global_model, local_model);
 }
 // return the version number of currently stored model
diff --git a/src/rabit.h b/src/rabit.h
index ac17faec6..cc65e62ae 100644
--- a/src/rabit.h
+++ b/src/rabit.h
@@ -6,6 +6,7 @@
  *   The actual implementation is redirected to rabit engine
  *   Code only using this header can also compiled with MPI Allreduce(with no fault recovery),
  *
+ *   rabit.h and serializable.h is all the user need to use rabit interface
  * \author Tianqi Chen, Ignacio Cano, Tianyi Zhou
  */
 #include <string>
@@ -14,9 +15,8 @@
 #if __cplusplus >= 201103L
 #include <functional>
 #endif // C++11
-// rabit headers
-#include "./io.h"
-#include "./engine.h"
+// contains definition of ISerializable
+#include "./serializable.h"
 
 /*! \brief namespace of rabit */
 namespace rabit {
@@ -31,7 +31,6 @@ struct Sum;
 /*! \brief perform bitwise OR */
 struct BitOR;
 }  // namespace op
-
 /*!
  * \brief intialize the rabit module, call this once function before using anything
  * \param argc number of arguments in argv
@@ -143,8 +142,8 @@ inline void Allreduce(DType *sendrecvbuf, size_t count, std::function<void()> pr
  *
  * \sa CheckPoint, VersionNumber
  */
-inline int LoadCheckPoint(utils::ISerializable *global_model,
-                          utils::ISerializable *local_model = NULL);
+inline int LoadCheckPoint(ISerializable *global_model,
+                          ISerializable *local_model = NULL);
 /*!
  * \brief checkpoint the model, meaning we finished a stage of execution
  *  every time we call check point, there is a version number which will increase by one
@@ -159,8 +158,8 @@ inline int LoadCheckPoint(utils::ISerializable *global_model,
    *       So only CheckPoint with global_model if possible
    * \sa LoadCheckPoint, VersionNumber
    */
-inline void CheckPoint(const utils::ISerializable *global_model,
-                       const utils::ISerializable *local_model = NULL);
+inline void CheckPoint(const ISerializable *global_model,
+                       const ISerializable *local_model = NULL);
 /*!
  * \return version number of current stored model,
  *         which means how many calls to CheckPoint we made so far
diff --git a/src/serializable.h b/src/serializable.h
new file mode 100644
index 000000000..a269dc1c7
--- /dev/null
+++ b/src/serializable.h
@@ -0,0 +1,99 @@
+#ifndef RABIT_SERIALIZABLE_H
+#define RABIT_SERIALIZABLE_H
+#include <vector>
+#include <string>
+#include "./utils.h"
+/*!
+ * \file serializable.h
+ * \brief defines serializable interface of rabit
+ * \author Tianqi Chen
+ */
+namespace rabit {
+/*!
+ * \brief interface of stream I/O, used by ISerializable
+ * \sa ISerializable
+ */
+class IStream {
+ public:
+  /*!
+   * \brief read data from stream
+   * \param ptr pointer to memory buffer
+   * \param size size of block
+   * \return usually is the size of data readed
+   */
+  virtual size_t Read(void *ptr, size_t size) = 0;
+  /*!
+   * \brief write data to stream
+   * \param ptr pointer to memory buffer
+   * \param size size of block
+   */
+  virtual void Write(const void *ptr, size_t size) = 0;
+  /*! \brief virtual destructor */
+  virtual ~IStream(void) {}
+
+ public:
+  // helper functions to write various of data structures
+  /*!
+   * \brief binary serialize a vector 
+   * \param vec vector to be serialized
+   */
+  template<typename T>
+  inline void Write(const std::vector<T> &vec) {
+    uint64_t sz = static_cast<uint64_t>(vec.size());
+    this->Write(&sz, sizeof(sz));
+    if (sz != 0) {
+      this->Write(&vec[0], sizeof(T) * sz);
+    }
+  }
+  /*!
+   * \brief binary load a vector 
+   * \param out_vec vector to be loaded
+   * \return whether load is successfull
+   */
+  template<typename T>
+  inline bool Read(std::vector<T> *out_vec) {
+    uint64_t sz;
+    if (this->Read(&sz, sizeof(sz)) == 0) return false;
+    out_vec->resize(sz);
+    if (sz != 0) {
+      if (this->Read(&(*out_vec)[0], sizeof(T) * sz) == 0) return false;
+    }
+    return true;
+  }
+  /*!
+   * \brief binary serialize a string
+   * \param str the string to be serialized
+   */ 
+  inline void Write(const std::string &str) {
+    uint64_t sz = static_cast<uint64_t>(str.length());
+    this->Write(&sz, sizeof(sz));
+    if (sz != 0) {
+      this->Write(&str[0], sizeof(char) * sz);
+    }
+  }
+  /*!
+   * \brief binary load a string
+   * \param out_str string to be loaded
+   * \return whether load is successful
+   */
+  inline bool Read(std::string *out_str) {
+    uint64_t sz;
+    if (this->Read(&sz, sizeof(sz)) == 0) return false;
+    out_str->resize(sz);
+    if (sz != 0) {
+      if (this->Read(&(*out_str)[0], sizeof(char) * sz) == 0) return false;
+    }
+    return true;
+  }
+};
+
+/*! \brief interface of se*/
+class ISerializable {
+ public:
+  /*! \brief load the model from file */
+  virtual void Load(IStream &fi) = 0;
+  /*! \brief save the model to the stream*/
+  virtual void Save(IStream &fo) const = 0;
+};
+}  // namespace rabit
+#endif
diff --git a/test/mock.h b/test/mock.h
index a5ac39c83..17e5b75c9 100644
--- a/test/mock.h
+++ b/test/mock.h
@@ -33,14 +33,14 @@ public:
     rabit::Allreduce<OP>(sendrecvbuf, count);
   }
 
-inline int LoadCheckPoint(utils::ISerializable *global_model,
-                          utils::ISerializable *local_model) {
+inline int LoadCheckPoint(ISerializable *global_model,
+                          ISerializable *local_model) {
     utils::Assert(verify(loadCheckpoint), "[%d] error when loading checkpoint", rank);
     return rabit::LoadCheckPoint(global_model, local_model);
   }
   
-  inline void CheckPoint(const utils::ISerializable *global_model,
-                         const utils::ISerializable *local_model) {
+  inline void CheckPoint(const ISerializable *global_model,
+                         const ISerializable *local_model) {
     utils::Assert(verify(checkpoint), "[%d] error when checkpointing", rank);
     rabit::CheckPoint(global_model, local_model);
   }
diff --git a/test/test_local_recover.cpp b/test/test_local_recover.cpp
index d98c6ae48..b9b84f2d1 100644
--- a/test/test_local_recover.cpp
+++ b/test/test_local_recover.cpp
@@ -29,16 +29,16 @@ inline void CallEnd(const char *fun, int ntrial, int iter) {
 }
 
 // dummy model
-class Model : public rabit::utils::ISerializable {
+class Model : public rabit::ISerializable {
  public:
   // iterations
   std::vector<float> data;
   // load from stream
-  virtual void Load(rabit::utils::IStream &fi) {
+  virtual void Load(rabit::IStream &fi) {
     fi.Read(&data);
   }
   /*! \brief save the model to the stream */
-  virtual void Save(rabit::utils::IStream &fo) const {
+  virtual void Save(rabit::IStream &fo) const {
     fo.Write(data);
   }
   virtual void InitModel(size_t n, float v) {
diff --git a/test/test_model_recover.cpp b/test/test_model_recover.cpp
index 6feb56dde..aba107a85 100644
--- a/test/test_model_recover.cpp
+++ b/test/test_model_recover.cpp
@@ -29,16 +29,16 @@ inline void CallEnd(const char *fun, int ntrial, int iter) {
 }
 
 // dummy model
-class Model : public rabit::utils::ISerializable {
+class Model : public rabit::ISerializable {
  public:
   // iterations
   std::vector<float> data;
   // load from stream
-  virtual void Load(rabit::utils::IStream &fi) {
+  virtual void Load(rabit::IStream &fi) {
     fi.Read(&data);
   }
   /*! \brief save the model to the stream */
-  virtual void Save(rabit::utils::IStream &fo) const {
+  virtual void Save(rabit::IStream &fo) const {
     fo.Write(data);
   }
   virtual void InitModel(size_t n) {
diff --git a/toolkit/kmeans.cpp b/toolkit/kmeans.cpp
index c08e50c23..bbd5067af 100644
--- a/toolkit/kmeans.cpp
+++ b/toolkit/kmeans.cpp
@@ -8,18 +8,18 @@
 using namespace rabit;
 
 // kmeans model
-class Model : public rabit::utils::ISerializable {
+class Model : public rabit::ISerializable {
  public:
   // matrix of centroids
   Matrix centroids;
   // load from stream
-  virtual void Load(rabit::utils::IStream &fi) {
+  virtual void Load(rabit::IStream &fi) {
     fi.Read(&centroids.nrow, sizeof(centroids.nrow));
     fi.Read(&centroids.ncol, sizeof(centroids.ncol));
     fi.Read(&centroids.data);
   }
   /*! \brief save the model to the stream */
-  virtual void Save(rabit::utils::IStream &fo) const {
+  virtual void Save(rabit::IStream &fo) const {
     fo.Write(&centroids.nrow, sizeof(centroids.nrow));
     fo.Write(&centroids.ncol, sizeof(centroids.ncol));
     fo.Write(centroids.data);
diff --git a/toolkit/toolkit_util.h b/toolkit/toolkit_util.h
index cff7b7fe0..a2f8f56ac 100644
--- a/toolkit/toolkit_util.h
+++ b/toolkit/toolkit_util.h
@@ -2,6 +2,7 @@
 #include <vector>
 #include <cstdlib>
 #include <cstdio>
+#include <cstring>
 #include <cmath>
 
 namespace rabit {