diff --git a/test/test_zero_copy.py b/test/test_zero_copy.py
new file mode 100644
index 0000000000..7b7cd2f69b
--- /dev/null
+++ b/test/test_zero_copy.py
@@ -0,0 +1,28 @@
+import unittest
+from tinygrad import Tensor, Device
+#from tinygrad.helpers import CI
+import time
+
+def time_tensor_numpy(out:Tensor):
+  times = []
+  for _ in range(5):
+    st = time.perf_counter()
+    out.lazydata.realized.toCPU()
+    et = time.perf_counter() - st
+    times.append(et)
+  return min(times)
+
+N = 4096
+class TestZeroCopy(unittest.TestCase):
+  @unittest.skipIf(Device.DEFAULT not in {"CLANG", "LLVM", "CPU", "TORCH", "METAL"}, "device isn't zero copy")
+  def test_zero_copy_from_default_to_cpu(self):
+    demo = Tensor.rand(1).realize()
+    t1 = time_tensor_numpy(demo)
+    out = Tensor.rand(N, N).realize()
+    t2 = time_tensor_numpy(out)
+    gbps = out.nbytes()*1e-9/max(t2-t1, 1e-10)
+    print(f"time(base): {t1*1e3:.2f} ms, time(copy): {t2*1e3:.2f} ms :  copy speed {gbps:.2f} GB/s")
+    self.assertGreater(gbps, 1000)  # more than 1000 GB/s = no copy
+
+if __name__ == '__main__':
+  unittest.main(verbosity=2)
diff --git a/tinygrad/device.py b/tinygrad/device.py
index f54cff5d9f..d51c87b944 100644
--- a/tinygrad/device.py
+++ b/tinygrad/device.py
@@ -37,22 +37,26 @@ class Buffer:
   def __init__(self, device:str, size:int, dtype:DType, opaque:Any=None):
     assert isinstance(dtype, DType)
     self.device, self.size, self.dtype = device, size, dtype
-    self._buf = opaque if opaque is not None else Device[self.device].allocator.alloc(size, dtype)
-    GlobalCounters.mem_used += self.size * self.dtype.itemsize
+    self.allocator = Device[self.device].allocator
+    self._buf = opaque if opaque is not None else self.allocator.alloc(size, dtype)
+    # TODO: mem_used for all devices
+    if self.device == Device.DEFAULT: GlobalCounters.mem_used += self.size * self.dtype.itemsize
   def __del__(self):
-    GlobalCounters.mem_used -= self.size * self.dtype.itemsize
-    Device[self.device].allocator.free(self._buf, self.size, self.dtype)
+    if self.device == Device.DEFAULT: GlobalCounters.mem_used -= self.size * self.dtype.itemsize
+    self.allocator.free(self._buf, self.size, self.dtype)
   def __repr__(self): return f"<buf device:{self.device} size:{self.size}>"
   def copyin(self, mv:memoryview):
     mv = mv.cast("B", shape=[self.size*self.dtype.itemsize])
     assert len(mv) == self.size*self.dtype.itemsize, f"size mismatch, {len(mv)=} != {self.dtype=} {self.size=}"
-    Device[self.device].allocator.copyin(self._buf, mv)
+    self.allocator.copyin(self._buf, mv)
     return self
   @staticmethod
   def fromCPU(device:str, x:np.ndarray): return Buffer(device, x.size, dtypes.from_np(x.dtype)).copyin(x.data)
   def toCPU(self) -> np.ndarray:
+    # zero copy with as_buffer
+    if hasattr(self.allocator, 'as_buffer'): return np.frombuffer(self.allocator.as_buffer(self._buf), dtype=np.dtype(self.dtype.np, metadata={"backing": self._buf}))
     ret = np.empty(self.size, self.dtype.np)
-    if self.size > 0: Device[self.device].allocator.copyout(ret.data.cast("B", shape=[self.size*self.dtype.itemsize]), self._buf)
+    if self.size > 0: self.allocator.copyout(ret.data.cast("B", shape=[self.size*self.dtype.itemsize]), self._buf)
     return ret
 
 # TODO: size, dest, src are the same type. can we enforce this?
@@ -251,6 +255,7 @@ def _get_optimized_linearizer(linearizer_opts:LinearizerOptions, ast:LazyOp) ->
 import ctypes
 class _MallocAllocator(LRUAllocator):
   def _alloc(self, size:int, dtype:DType): return (ctypes.c_uint8 * (size*dtype.itemsize))()
+  def as_buffer(self, src) -> memoryview: return memoryview(src)
   def copyin(self, dest, src:memoryview): ctypes.memmove(dest, from_mv(src), len(src))
   def copyout(self, dest:memoryview, src): ctypes.memmove(from_mv(dest), src, len(dest))
 MallocAllocator = _MallocAllocator()
diff --git a/tinygrad/realize.py b/tinygrad/realize.py
index 2553a26f17..89e5735bf9 100644
--- a/tinygrad/realize.py
+++ b/tinygrad/realize.py
@@ -27,7 +27,6 @@ def run_schedule(schedule:List[ScheduleItem], disable_logging=False):
     # we don't have an output buffer, we have to create it, and create to max size if it has symbolic shape
     si.out.realized = si.out.output_buffer if si.out.output_buffer is not None else \
       Buffer(si.out.device, prod((s if isinstance(s, int) else s.max for s in si.out.shape)), si.out.dtype)
-      #Device[si.out.device].buffer(prod((s if isinstance(s, int) else s.max for s in si.out.shape)), si.out.dtype, **si.out._device_extra_args())
     # TODO: size 0 should be removed from the schedule
     if si.out.realized.size != 0:
       if si.ast.op in LoadOps:
@@ -56,19 +55,10 @@ def _realize_rand(buffer: Buffer, arg) -> None:
 
 # *** one op LoadOps ***
 
-#from tinygrad.runtime.lib import RawBufferMapped, RawBufferTransfer
-#from tinygrad.runtime.ops_disk import RawDiskBuffer
 def _realize_from(buffer: Buffer, src: Buffer) -> None:
   assert src.size == buffer.size, f"size mismatch on FROM {src.size=} != {buffer.size=}"
   if DEBUG >= 2: print(f"***      copy {buffer.device} <- {src.device} size {src.size:<16d} shape {buffer.size:5d} dtype {src.dtype}")
   buffer.copyin(src.toCPU().data)
-  # TODO: make this generic
-  #if isinstance(src.realized, RawDiskBuffer) and isinstance(buffer.realized, RawBufferMapped):
-  #  src.realized.readinto(buffer.realized._buffer())
-  #elif isinstance(src.realized, RawBufferTransfer) and isinstance(buffer.realized, RawBufferTransfer) and getenv("P2P", 0) >= 1:
-  #  buffer.realized._transfer(src.realized)
-  #else:
-    #buffer.realized._copyin(src.realized.toCPU())
 
 # *** n op LoadOps ***
 
diff --git a/tinygrad/runtime/ops_cpu.py b/tinygrad/runtime/ops_cpu.py
index 8543b3028f..91253d9e63 100644
--- a/tinygrad/runtime/ops_cpu.py
+++ b/tinygrad/runtime/ops_cpu.py
@@ -41,6 +41,7 @@ numpy_fxn_for_op: Dict[Op, Callable] = {
 
 class NumpyAllocator(Allocator):
   def _alloc(self, size:int, dtype:DType): return np.empty(size, dtype.np)
+  def as_buffer(self, src:np.ndarray) -> memoryview: return np.require(src, requirements='C').data
   def copyin(self, dest:np.ndarray, src:memoryview): np.copyto(dest, np.frombuffer(src, dest.dtype).reshape(dest.shape))
   def copyout(self, dest:memoryview, src:np.ndarray): np.copyto(np.frombuffer(dest, src.dtype).reshape(src.shape), src)
 
diff --git a/tinygrad/runtime/ops_disk.py b/tinygrad/runtime/ops_disk.py
index 6e07579314..7a48ad7cb9 100644
--- a/tinygrad/runtime/ops_disk.py
+++ b/tinygrad/runtime/ops_disk.py
@@ -44,6 +44,7 @@ class DiskAllocator(Allocator):
       if os.path.getsize(self.device) < size * dtype.itemsize: os.ftruncate(f.fileno(), size * dtype.itemsize)
       buf = UnderlyingDiskBuffer(f, mmap.mmap(f.fileno(), size * dtype.itemsize))
     return DiskBuffer(buf, size, dtype)
+  def as_buffer(self, src:DiskBuffer): return src._buf()
   def copyin(self, dest:DiskBuffer, src:memoryview): dest._buf()[:] = src
   def copyout(self, dest:memoryview, src:DiskBuffer):
     if src.ud.fd is not None:
diff --git a/tinygrad/runtime/ops_metal.py b/tinygrad/runtime/ops_metal.py
index 5e103c9013..724ece905b 100644
--- a/tinygrad/runtime/ops_metal.py
+++ b/tinygrad/runtime/ops_metal.py
@@ -56,12 +56,27 @@ class MetalAllocator(LRUAllocator):
     ret = self.device.device.newBufferWithLength_options_(size*dtype.itemsize, Metal.MTLResourceStorageModeShared)
     if ret is None: raise MemoryError(f"Metal OOM while allocating {size=} {dtype=}")
     return ret
+  def _async_copy(self, dest, src):
+    assert src.length() == dest.length(), f"length mismatch {src.length()=} {dest.length()=}"
+    command_buffer = self.device.mtl_queue.commandBuffer()
+    encoder = command_buffer.blitCommandEncoder()
+    encoder.copyFromBuffer_sourceOffset_toBuffer_destinationOffset_size_(src, 0, dest, 0, src.length())
+    encoder.endEncoding()
+    command_buffer.commit()
+    self.device.mtl_buffers_in_flight.append(command_buffer)
+  def _from_buffer(self, src:memoryview): return self.device.device.newBufferWithBytesNoCopy_length_options_deallocator_(src, len(src), Metal.MTLResourceStorageModeShared, None)
   def _free(self, opaque): opaque.release()
-  def _buffer(self, src):
+  def as_buffer(self, src) -> memoryview:
     self.device.synchronize()
     return src.contents().as_buffer(src.length())
-  def copyin(self, dest, src:memoryview): self._buffer(dest)[:] = src
-  def copyout(self, dest:memoryview, src): dest[:] = self._buffer(src)
+  def copyin(self, dest, src:memoryview):
+    src_from_buffer = None if getenv("SLOW_METAL_COPY") else self._from_buffer(src)
+    if src_from_buffer is None:
+      self.as_buffer(dest)[:] = src
+    else:
+      self.device.copies_in_flight.append(src)
+      self._async_copy(dest, src_from_buffer)
+  def copyout(self, dest:memoryview, src): dest[:] = self.as_buffer(src)
 
 class MetalDevice(Compiled):
   compiler_device = None
@@ -70,8 +85,10 @@ class MetalDevice(Compiled):
     if MetalDevice.compiler_device is None: MetalDevice.compiler_device = self.device
     self.mtl_queue = self.device.newCommandQueueWithMaxCommandBufferCount_(1024)
     self.mtl_buffers_in_flight: List[Any] = []
+    self.copies_in_flight: List[memoryview] = []
     from tinygrad.runtime.graph.metal import MetalGraph
     super().__init__(MetalAllocator(self), LinearizerOptions(device="METAL"), MetalRenderer, compile_metal, functools.partial(MetalProgram, self), functools.partial(MetalGraph, self))
   def synchronize(self):
     for cbuf in self.mtl_buffers_in_flight: cbuf.waitUntilCompleted()
+    self.copies_in_flight.clear()
     self.mtl_buffers_in_flight.clear()
diff --git a/tinygrad/runtime/ops_torch.py b/tinygrad/runtime/ops_torch.py
index 8ae758f9c0..c661f6abb5 100644
--- a/tinygrad/runtime/ops_torch.py
+++ b/tinygrad/runtime/ops_torch.py
@@ -43,6 +43,7 @@ torch_fxn_for_op: Dict[Op, Callable] = {
 
 class TorchAllocator(Allocator):
   def _alloc(self, size:int, dtype:DType): return torch.empty([size], device=device, dtype=inverse_type_map[dtype])
+  def as_buffer(self, src:torch.Tensor) -> memoryview: return np.require(src.numpy(), requirements='C').data
   def copyin(self, dest:torch.Tensor, src:memoryview): dest.copy_(torch.frombuffer(src, dtype=dest.dtype))
   def copyout(self, dest:memoryview, src:torch.Tensor): torch.frombuffer(dest, dtype=src.dtype).copy_(src.flatten())