diff --git a/src/unix/async_io.ml b/src/io/async_io.ml
similarity index 100%
rename from src/unix/async_io.ml
rename to src/io/async_io.ml
diff --git a/src/unix/async_io.mli b/src/io/async_io.mli
similarity index 100%
rename from src/unix/async_io.mli
rename to src/io/async_io.mli
diff --git a/src/unix/cancel_handle.ml b/src/io/cancel_handle.ml
similarity index 100%
rename from src/unix/cancel_handle.ml
rename to src/io/cancel_handle.ml
diff --git a/src/unix/cancel_handle.mli b/src/io/cancel_handle.mli
similarity index 100%
rename from src/unix/cancel_handle.mli
rename to src/io/cancel_handle.mli
diff --git a/src/unix/common_.ml b/src/io/common_.ml
similarity index 100%
rename from src/unix/common_.ml
rename to src/io/common_.ml
diff --git a/src/unix/dune b/src/io/dune
similarity index 100%
rename from src/unix/dune
rename to src/io/dune
diff --git a/src/unix/ev_loop.ml b/src/io/ev_loop.ml
similarity index 100%
rename from src/unix/ev_loop.ml
rename to src/io/ev_loop.ml
diff --git a/src/unix/ev_loop.mli b/src/io/ev_loop.mli
similarity index 100%
rename from src/unix/ev_loop.mli
rename to src/io/ev_loop.mli
diff --git a/src/unix/fd.ml b/src/io/fd.ml
similarity index 100%
rename from src/unix/fd.ml
rename to src/io/fd.ml
diff --git a/src/unix/heap_.ml b/src/io/heap_.ml
similarity index 100%
rename from src/unix/heap_.ml
rename to src/io/heap_.ml
diff --git a/src/unix/heap_.mli b/src/io/heap_.mli
similarity index 100%
rename from src/unix/heap_.mli
rename to src/io/heap_.mli
diff --git a/src/io/moonpool_io.ml b/src/io/moonpool_io.ml
new file mode 100644
index 00000000..cde342f2
--- /dev/null
+++ b/src/io/moonpool_io.ml
@@ -0,0 +1,20 @@
+(** {2 Re-exports} *)
+
+module Exn_bt = Moonpool.Exn_bt
+module Fiber = Moonpool_fib.Fiber
+module FLS = Moonpool_fib.Fls
+module Runner = Moonpool.Runner
+module Ws_pool = Moonpool.Ws_pool
+module Fifo_pool = Moonpool.Fifo_pool
+module Fut = Moonpool.Fut
+
+(** {2 Event loop modules} *)
+
+module Fd = Fd
+module Cancel_handle = Cancel_handle
+module Sockaddr = Sockaddr
+include Async_io
+
+let run_after_s = Ev_loop.run_after_s
+let run_every_s = Ev_loop.run_every_s
+let main = Moonpool_fib.main
diff --git a/src/unix/sockaddr.ml b/src/io/sockaddr.ml
similarity index 100%
rename from src/unix/sockaddr.ml
rename to src/io/sockaddr.ml
diff --git a/src/unix/time.mli b/src/io/time.mli
similarity index 100%
rename from src/unix/time.mli
rename to src/io/time.mli
diff --git a/src/unix/time.mtime.ml b/src/io/time.mtime.ml
similarity index 100%
rename from src/unix/time.mtime.ml
rename to src/io/time.mtime.ml
diff --git a/src/unix/time.unix.ml b/src/io/time.unix.ml
similarity index 100%
rename from src/unix/time.unix.ml
rename to src/io/time.unix.ml
diff --git a/src/unix/timer.ml b/src/io/timer.ml
similarity index 100%
rename from src/unix/timer.ml
rename to src/io/timer.ml
diff --git a/src/unix/timer.mli b/src/io/timer.mli
similarity index 100%
rename from src/unix/timer.mli
rename to src/io/timer.mli
diff --git a/test/io/dune b/test/io/dune
new file mode 100644
index 00000000..77e9b19c
--- /dev/null
+++ b/test/io/dune
@@ -0,0 +1,4 @@
+(executables
+ (names t_hash echo_server)
+ ;(package moonpool-unix)
+ (libraries moonpool moonpool-io trace.core trace-tef))
diff --git a/test/io/echo_server.ml b/test/io/echo_server.ml
new file mode 100644
index 00000000..da2c30c2
--- /dev/null
+++ b/test/io/echo_server.ml
@@ -0,0 +1,62 @@
+module M = Moonpool
+module MU = Moonpool_io
+module Trace = Trace_core
+
+let ( let@ ) = ( @@ )
+
+let main ~port ~j () : unit =
+  let@ _sp = Trace.with_span ~__FILE__ ~__LINE__ "main" in
+  let@ runner = M.Ws_pool.with_ ~name:"tpool" ~num_threads:j () in
+
+  let@ _main_runner = MU.main in
+  Trace.set_thread_name "main";
+
+  let@ server =
+    MU.TCP_server.with_server ~runner (MU.Sockaddr.any port)
+      ~handle:(fun ~client_addr:addr ic oc ->
+        Trace.message "got new client";
+        let@ _sp =
+          Trace.with_span ~__FILE__ ~__LINE__ "handle.client" ~data:(fun () ->
+              [ "addr", `String (MU.Sockaddr.show addr) ])
+        in
+
+        let buf = Bytes.create 32 in
+        let continue = ref true in
+        while !continue do
+          Trace.message "read";
+          let n = Iostream.In_buf.input ic buf 0 (Bytes.length buf) in
+          if n = 0 then continue := false;
+          Trace.messagef (fun k -> k "got %dB" n);
+          Iostream.Out_buf.output oc buf 0 n;
+          Iostream.Out_buf.flush oc;
+          Trace.message "write"
+          (* MU.sleep_s 0.02 *)
+        done)
+  in
+
+  Trace.messagef (fun k ->
+      k "server established on %s"
+        (MU.Sockaddr.show @@ MU.TCP_server.endpoint server));
+  Printf.printf "listening on %s\n%!"
+    (MU.Sockaddr.show @@ MU.TCP_server.endpoint server);
+
+  Trace.message "awaiting server";
+  MU.TCP_server.await server;
+  ()
+
+let () =
+  Sys.catch_break true;
+  let@ () = Trace_tef.with_setup () in
+  Trace.set_thread_name "entry";
+  let port = ref 0 in
+  let j = ref 4 in
+
+  let opts =
+    [
+      "-p", Arg.Set_int port, " port"; "j", Arg.Set_int j, " number of threads";
+    ]
+    |> Arg.align
+  in
+  Arg.parse opts ignore "echo server";
+
+  main ~port:!port ~j:!j ()
diff --git a/test/io/t_hash.ml b/test/io/t_hash.ml
new file mode 100644
index 00000000..4adbbbe5
--- /dev/null
+++ b/test/io/t_hash.ml
@@ -0,0 +1,154 @@
+(* vendored from https://github.com/dbuenzli/uuidm *)
+
+let sha_1 s =
+  (* Based on pseudo-code of RFC 3174. Slow and ugly but does the job. *)
+  let sha_1_pad s =
+    let len = String.length s in
+    let blen = 8 * len in
+    let rem = len mod 64 in
+    let mlen =
+      if rem > 55 then
+        len + 128 - rem
+      else
+        len + 64 - rem
+    in
+    let m = Bytes.create mlen in
+    Bytes.blit_string s 0 m 0 len;
+    Bytes.fill m len (mlen - len) '\x00';
+    Bytes.set m len '\x80';
+    if Sys.word_size > 32 then (
+      Bytes.set m (mlen - 8) (Char.unsafe_chr ((blen lsr 56) land 0xFF));
+      Bytes.set m (mlen - 7) (Char.unsafe_chr ((blen lsr 48) land 0xFF));
+      Bytes.set m (mlen - 6) (Char.unsafe_chr ((blen lsr 40) land 0xFF));
+      Bytes.set m (mlen - 5) (Char.unsafe_chr ((blen lsr 32) land 0xFF))
+    );
+    Bytes.set m (mlen - 4) (Char.unsafe_chr ((blen lsr 24) land 0xFF));
+    Bytes.set m (mlen - 3) (Char.unsafe_chr ((blen lsr 16) land 0xFF));
+    Bytes.set m (mlen - 2) (Char.unsafe_chr ((blen lsr 8) land 0xFF));
+    Bytes.set m (mlen - 1) (Char.unsafe_chr (blen land 0xFF));
+    m
+  in
+  (* Operations on int32 *)
+  let ( &&& ) = ( land ) in
+  let ( lor ) = Int32.logor in
+  let ( lxor ) = Int32.logxor in
+  let ( land ) = Int32.logand in
+  let ( ++ ) = Int32.add in
+  let lnot = Int32.lognot in
+  let sr = Int32.shift_right in
+  let sl = Int32.shift_left in
+  let cls n x = sl x n lor Int32.shift_right_logical x (32 - n) in
+  (* Start *)
+  let m = sha_1_pad s in
+  let w = Array.make 16 0l in
+  let h0 = ref 0x67452301l in
+  let h1 = ref 0xEFCDAB89l in
+  let h2 = ref 0x98BADCFEl in
+  let h3 = ref 0x10325476l in
+  let h4 = ref 0xC3D2E1F0l in
+  let a = ref 0l in
+  let b = ref 0l in
+  let c = ref 0l in
+  let d = ref 0l in
+  let e = ref 0l in
+  for i = 0 to (Bytes.length m / 64) - 1 do
+    (* For each block *)
+    (* Fill w *)
+    let base = i * 64 in
+    for j = 0 to 15 do
+      let k = base + (j * 4) in
+      w.(j) <-
+        sl (Int32.of_int (Char.code @@ Bytes.get m k)) 24
+        lor sl (Int32.of_int (Char.code @@ Bytes.get m (k + 1))) 16
+        lor sl (Int32.of_int (Char.code @@ Bytes.get m (k + 2))) 8
+        lor Int32.of_int (Char.code @@ Bytes.get m (k + 3))
+    done;
+    (* Loop *)
+    a := !h0;
+    b := !h1;
+    c := !h2;
+    d := !h3;
+    e := !h4;
+    for t = 0 to 79 do
+      let f, k =
+        if t <= 19 then
+          !b land !c lor (lnot !b land !d), 0x5A827999l
+        else if t <= 39 then
+          !b lxor !c lxor !d, 0x6ED9EBA1l
+        else if t <= 59 then
+          !b land !c lor (!b land !d) lor (!c land !d), 0x8F1BBCDCl
+        else
+          !b lxor !c lxor !d, 0xCA62C1D6l
+      in
+      let s = t &&& 0xF in
+      if t >= 16 then
+        w.(s) <-
+          cls 1
+            (w.(s + 13 &&& 0xF)
+            lxor w.(s + 8 &&& 0xF)
+            lxor w.(s + 2 &&& 0xF)
+            lxor w.(s));
+      let temp = cls 5 !a ++ f ++ !e ++ w.(s) ++ k in
+      e := !d;
+      d := !c;
+      c := cls 30 !b;
+      b := !a;
+      a := temp
+    done;
+    (* Update *)
+    h0 := !h0 ++ !a;
+    h1 := !h1 ++ !b;
+    h2 := !h2 ++ !c;
+    h3 := !h3 ++ !d;
+    h4 := !h4 ++ !e
+  done;
+  let h = Bytes.create 20 in
+  let i2s h k i =
+    Bytes.set h k (Char.unsafe_chr (Int32.to_int (sr i 24) &&& 0xFF));
+    Bytes.set h (k + 1) (Char.unsafe_chr (Int32.to_int (sr i 16) &&& 0xFF));
+    Bytes.set h (k + 2) (Char.unsafe_chr (Int32.to_int (sr i 8) &&& 0xFF));
+    Bytes.set h (k + 3) (Char.unsafe_chr (Int32.to_int i &&& 0xFF))
+  in
+  i2s h 0 !h0;
+  i2s h 4 !h1;
+  i2s h 8 !h2;
+  i2s h 12 !h3;
+  i2s h 16 !h4;
+  Bytes.unsafe_to_string h
+
+(*---------------------------------------------------------------------------
+   Copyright (c) 2008 The uuidm programmers
+
+   Permission to use, copy, modify, and/or distribute this software for any
+   purpose with or without fee is hereby granted, provided that the above
+   copyright notice and this permission notice appear in all copies.
+
+   THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+   WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+   MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+   ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+   WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+   ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+   OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+  ---------------------------------------------------------------------------*)
+
+module M = Moonpool
+module MU = Moonpool_unix
+
+type state = {
+  runner: M.Runner.t;
+  hashes: (string, string) Hashtbl.t M.Lock.t;
+  delay: float;
+}
+
+(*
+let hash_dir ~runner (d:string) =
+  if not (Sys.exists d) then ""
+  else
+  if Sys.is_directory d then (
+
+    let children = List.map
+
+  )
+
+  *)