diff --git a/knob.cabal b/knob.cabal
--- a/knob.cabal
+++ b/knob.cabal
@@ -1,6 +1,6 @@
 cabal-version: 2.4
 name: knob
-version: 0.2
+version: 0.2.1
 license: MIT
 license-file: license.txt
 author: John Millikin <jmillikin@gmail.com>
diff --git a/lib/Data/Knob.hs b/lib/Data/Knob.hs
--- a/lib/Data/Knob.hs
+++ b/lib/Data/Knob.hs
@@ -5,11 +5,11 @@
 -- Copyright: 2011 John Millikin
 -- License: MIT
 --
--- Maintainer: jmillikin@gmail.com
+-- Maintainer: n@monade.li
 -- Portability: GHC only
 --
--- Create memory&#8208;backed 'IO.Handle's, referencing virtual files. This is
--- mostly useful for testing 'IO.Handle'&#8208;based APIs without having to
+-- Create memory-backed 'IO.Handle's, referencing virtual files. This is
+-- mostly useful for testing 'IO.Handle'-based APIs without having to
 -- interact with the filesystem.
 --
 -- > import Data.ByteString (pack)
@@ -112,11 +112,34 @@
     padLen | padLen > 0 -> Data.ByteString.append bytes (Data.ByteString.replicate padLen 0)
     _ -> Data.ByteString.take intSize bytes
 
+{- What about non-POSIX environment? -}
 instance IO.RawIO Device where
-  read             = error "Raw IO is not implemented for knobs"
-  readNonBlocking  = error "Raw IO is not implemented for knobs"
-  write            = error "Raw IO is not implemented for knobs"
-  writeNonBlocking = error "Raw IO is not implemented for knobs"
+  read (Device _ bytes_var pos_var) ptr _ bufSize = do
+    MVar.withMVar bytes_var $ \bytes -> do
+      MVar.modifyMVar pos_var $ \pos -> do
+        if pos >= Data.ByteString.length bytes
+          then return (pos, 0)
+          else do
+            let chunk = Data.ByteString.take bufSize (Data.ByteString.drop pos bytes)
+            unsafeUseAsCStringLen chunk $ \(chunkPtr, chunkLen) -> do
+              Foreign.copyArray ptr (Foreign.castPtr chunkPtr) chunkLen
+              return (pos + chunkLen, chunkLen)
+
+  write (Device _ bytes_var pos_var) ptr _ bufSize = do
+    MVar.modifyMVar_ bytes_var $ \bytes -> do
+      MVar.modifyMVar pos_var $ \pos -> do
+        let (before, after) = Data.ByteString.splitAt pos bytes
+        let padding = Data.ByteString.replicate (pos - Data.ByteString.length before) 0
+
+        bufBytes <- Data.ByteString.packCStringLen (Foreign.castPtr ptr, bufSize)
+        let newBytes = Data.ByteString.concat [before, padding, bufBytes, Data.ByteString.drop bufSize after]
+        return (pos + bufSize, newBytes)
+    return ()
+
+  readNonBlocking dev buf off size = IO.read dev buf off size >>= \cnt -> if cnt == 0
+    then return Nothing
+    else return $ Just cnt
+  writeNonBlocking dev buf off cnt = IO.write dev buf off cnt >> return cnt
 
 instance IO.BufferedIO Device where
   newBuffer _ = IO.newByteBuffer 4096