diff --git a/src/ikarus.boot b/src/ikarus.boot
index 3e060b2..9bfe9bb 100644
Binary files a/src/ikarus.boot and b/src/ikarus.boot differ
diff --git a/src/ikarus.io-ports.ss b/src/ikarus.io-ports.ss
index ad29203..210f69c 100644
--- a/src/ikarus.io-ports.ss
+++ b/src/ikarus.io-ports.ss
@@ -10,6 +10,7 @@
   (import 
     (ikarus system $ports)
     (ikarus system $strings)
+    (ikarus system $bytevectors)
     (ikarus system $fx)
     (except (ikarus)  make-input-port make-output-port 
          make-input/output-port port-handler
@@ -52,14 +53,14 @@
   ;;;
   (define $make-input-port
     (lambda (handler buffer)
-      ($make-port/input handler buffer 0 (string-length buffer) #f 0 0)))
+      ($make-port/input handler buffer 0 ($bytevector-length buffer) #f 0 0)))
   ;;;
   (define make-input-port
     (lambda (handler buffer)
       (if (procedure? handler)
-          (if (string? buffer)
+          (if (bytevector? buffer)
               ($make-input-port handler buffer)
-              (error 'make-input-port "~s is not a string" buffer))
+              (error 'make-input-port "~s is not a bytevector" buffer))
           (error 'make-input-port "~s is not a procedure" handler))))
   ;;;
   (define $make-output-port
@@ -77,19 +78,19 @@
   (define $make-input/output-port
     (lambda (handler input-buffer output-buffer)
        ($make-port/both handler
-                  input-buffer 0 (string-length input-buffer)
+                  input-buffer 0 ($bytevector-length input-buffer)
                   output-buffer 0 (string-length output-buffer))))
   ;;;
   (define make-input/output-port
     (lambda (handler input-buffer output-buffer)
       (if (procedure? handler)
-          (if (string? input-buffer)
+          (if (bytevector? input-buffer)
               (if (string? output-buffer)
                   ($make-input/output-port handler input-buffer output-buffer) 
                   (error 'make-input/output-port 
                          "~s is not a string"
                          output-buffer))
-              (error 'make-input/output-port "~s is not a string" input-buffer))
+              (error 'make-input/output-port "~s is not a bytevector" input-buffer))
           (error 'make-input/output-port "~s is not a procedure" handler))))
   ;;;
   (define port-handler
@@ -151,7 +152,7 @@
       (if (input-port? p)
           (if (fixnum? i)
               (if ($fx>= i 0)
-                  (if ($fx<= i (string-length ($port-input-buffer p)))
+                  (if ($fx<= i ($bytevector-length ($port-input-buffer p)))
                       (begin
                         ($set-port-input-index! p 0)
                         ($set-port-input-size! p i))
diff --git a/src/ikarus.io-primitives.unsafe.ss b/src/ikarus.io-primitives.unsafe.ss
index fcd81c9..beedfee 100644
--- a/src/ikarus.io-primitives.unsafe.ss
+++ b/src/ikarus.io-primitives.unsafe.ss
@@ -7,6 +7,8 @@
     (ikarus)
     (ikarus system $ports)
     (ikarus system $strings)
+    (ikarus system $chars)
+    (ikarus system $bytevectors)
     (ikarus system $fx))
 
   (define $write-char
@@ -22,27 +24,35 @@
     (lambda (p)
       (let ([idx ($port-input-index p)])
         (if ($fx< idx ($port-input-size p))
-            (begin
-              ($set-port-input-index! p ($fxadd1 idx))
-              (string-ref ($port-input-buffer p) idx))
-            (begin
-              (($port-handler p) 'read-char p))))))
+            (let ([b ($bytevector-u8-ref ($port-input-buffer p) idx)])
+              (cond
+                [($fx<= b 127) 
+                 ($set-port-input-index! p ($fxadd1 idx))
+                 ($fixnum->char b)]
+                [else (($port-handler p) 'read-char p)]))
+            (($port-handler p) 'read-char p)))))
 
   (define $peek-char
     (lambda (p)
       (let ([idx ($port-input-index p)])
         (if ($fx< idx ($port-input-size p))
-            (string-ref ($port-input-buffer p) idx)
+            (let ([b ($bytevector-u8-ref ($port-input-buffer p) idx)])
+                (cond
+                  [($fx<= b 127) 
+                   ($fixnum->char b)]
+                  [else (($port-handler p) 'peek-char p)]))
             (($port-handler p) 'peek-char p)))))
 
   (define $unread-char
     (lambda (c p)
-      (let ([idx ($fxsub1 ($port-input-index p))])
-        (if (and ($fx>= idx 0)
+      (let ([idx ($fxsub1 ($port-input-index p))]
+            [b ($char->fixnum c)])
+        (if (and ($fx<= b 127)
+                 ($fx>= idx 0)
                  ($fx< idx ($port-input-size p)))
             (begin
               ($set-port-input-index! p idx)
-              (string-set! ($port-input-buffer p) idx c))
+              ($bytevector-set! ($port-input-buffer p) idx b))
             (($port-handler p) 'unread-char c p)))))
 
   (define $reset-input-port!
diff --git a/src/ikarus.io.input-files.ss b/src/ikarus.io.input-files.ss
index e59fbf4..27c0870 100644
--- a/src/ikarus.io.input-files.ss
+++ b/src/ikarus.io.input-files.ss
@@ -7,6 +7,7 @@
     (ikarus system $io)
     (ikarus system $fx)
     (ikarus system $strings)
+    (ikarus system $bytevectors)
     (ikarus system $chars)
     (except (ikarus)
             open-input-file current-input-port console-input-port
@@ -45,7 +46,7 @@
            (close-input-port p)
            (close-ports))])))
  
-  (define make-input-file-handler
+  (define make-input-file-handler-old
     (lambda (fd port-name)
       (let ((open? #t))
         (lambda (msg . args)
@@ -118,6 +119,72 @@
              (error 'input-file-handler
                     "message not handled ~s" (cons msg args))])))))
 
+  (define make-input-file-handler
+    (lambda (fd port-name)
+      (let ([open? #t] [idx 0] [size 0] [buff (make-string 4096)])
+        (lambda (msg . args)
+          (message-case msg args
+            [(read-char p)
+             (unless (input-port? p)
+               (error 'read-char "~s is not an input port" p))
+             (if ($fx< idx size)
+                 (let ([c (string-ref buff idx)])
+                   (set! idx ($fxadd1 idx))
+                   c)
+                 (if open?
+                     (let ([bytes
+                            (foreign-call "ikrt_read" fd buff)])
+                       (cond
+                         [($fx> bytes 0)
+                          (set! size bytes)
+                          (set! idx 1)
+                          ($string-ref buff 0)]
+                         [($fx= bytes 0)
+                          (eof-object)]
+                         [else
+                          (error 'read-char "Cannot read from ~a"
+                                 port-name)]))
+                     (error 'read-char "port ~s is closed" p)))]
+            [(peek-char p)
+             (unless (input-port? p)
+               (error 'peek-char "~s is not an input port" p))
+             (if ($fx< idx size)
+                 (string-ref buff idx)
+                 (if open?
+                     (let ([bytes
+                            (foreign-call "ikrt_read" fd buff)])
+                       (cond
+                         [(not bytes)
+                          (error 'peek-char
+                                 "Cannot read from ~s" port-name)]
+                         [($fx= bytes 0)
+                          (eof-object)]
+                         [else
+                          (set! size bytes)
+                          (string-ref buff 0)]))
+                     (error 'peek-char "port ~s is closed" p)))]
+            [(unread-char c p)
+             (unless (input-port? p)
+               (error 'unread-char "~s is not an input port" p))
+             (let ([i ($fxsub1 idx)])
+               (if (and ($fx>= i 0) ($fx< i size))
+                   (set! idx i)
+                   (if open?
+                       (error 'unread-char "port ~s is closed" p)
+                       (error 'unread-char "too many unread-chars"))))]
+            [(port-name p) port-name]
+            [(close-port p)
+             (unless (input-port? p)
+               (error 'close-input-port "~s is not an input port" p))
+             (when open?
+               (set! size 0)
+               (set! open? #f)
+               (unless (foreign-call "ikrt_close_file" fd)
+                  (error 'close-input-port "cannot close ~s" port-name)))]
+            [else 
+             (error 'input-file-handler
+                    "message not handled ~s" (cons msg args))])))))
+
   (define $open-input-file
     (lambda (filename)
       (close-ports)
@@ -125,8 +192,8 @@
         (if (fixnum? fd/error)
             (let ([port (make-input-port 
                           (make-input-file-handler fd/error filename)
-                          (make-string 4096))])
-              (set-port-input-size! port 0)
+                          ($make-bytevector 0))])
+              ;(set-port-input-size! port 0)
               (guardian port)
               port)
             (error 'open-input-file "cannot open ~s: ~a" filename fd/error)))))
@@ -185,8 +252,8 @@
   (set! *standard-input-port* 
     (let ([p (make-input-port 
                (make-input-file-handler 0 '*stdin*)
-               (make-string 4096))])
-      (set-port-input-size! p 0)
+               ($make-bytevector 0))])
+      ;(set-port-input-size! p 0)
       p))
   (set! *current-input-port* *standard-input-port*)
   )
diff --git a/src/ikarus.io.input-strings.ss b/src/ikarus.io.input-strings.ss
index fd8b0af..22fab19 100644
--- a/src/ikarus.io.input-strings.ss
+++ b/src/ikarus.io.input-strings.ss
@@ -3,6 +3,7 @@
   (export open-input-string)
   (import 
     (ikarus system $strings)
+    (ikarus system $bytevectors)
     (ikarus system $fx)
     (ikarus system $pairs)
     (ikarus system $ports)
@@ -72,7 +73,7 @@
         (error 'open-input-string "~s is not a string" str))
       (let ([port (make-input-port
                     (make-input-string-handler str)
-                    "")])
+                    ($make-bytevector 0))])
         port)))
   )