diff --git a/emulator/core/src/debugger.rs b/emulator/core/src/debugger.rs
index 8280e8d..c2ff630 100644
--- a/emulator/core/src/debugger.rs
+++ b/emulator/core/src/debugger.rs
@@ -3,7 +3,7 @@ use std::io::Write;
 
 use crate::error::Error;
 use crate::system::System;
-use crate::devices::{Address, Addressable, Debuggable, TransmutableBox};
+use crate::devices::{Address, Addressable, Debuggable, Device};
 
 
 #[derive(Default)]
@@ -19,7 +19,7 @@ impl Debugger {
         self.trace_only = false;
     }
 
-    pub fn run_debugger(&mut self, system: &System, target: TransmutableBox) -> Result<(), Error> {
+    pub fn run_debugger(&mut self, system: &System, target: Device) -> Result<(), Error> {
         let mut target = target.borrow_mut();
         let debug_obj = target.as_debuggable().unwrap();
         println!("@ {} ns", system.clock.as_duration().as_nanos());
diff --git a/emulator/core/src/devices.rs b/emulator/core/src/devices.rs
index 7d0ef76..50b6872 100644
--- a/emulator/core/src/devices.rs
+++ b/emulator/core/src/devices.rs
@@ -1,6 +1,7 @@
 
 use std::rc::Rc;
-use std::cell::RefCell;
+use std::cell::{RefCell, RefMut, BorrowMutError};
+use std::sync::atomic::{AtomicUsize, Ordering};
 
 use crate::error::Error;
 use crate::system::System;
@@ -28,6 +29,7 @@ pub trait Interruptable {
 
 /// A device that can be addressed to read data from or write data to the device.
 pub trait Addressable {
+    #[inline]
     fn size(&self) -> usize;
     fn read(&mut self, clock: ClockTime, addr: Address, data: &mut [u8]) -> Result<(), Error>;
     fn write(&mut self, clock: ClockTime, addr: Address, data: &[u8]) -> Result<(), Error>;
@@ -174,22 +176,27 @@ pub trait Inspectable {
 
 
 pub trait Transmutable {
+    #[inline]
     fn as_steppable(&mut self) -> Option<&mut dyn Steppable> {
         None
     }
 
+    #[inline]
     fn as_addressable(&mut self) -> Option<&mut dyn Addressable> {
         None
     }
 
+    #[inline]
     fn as_interruptable(&mut self) -> Option<&mut dyn Interruptable> {
         None
     }
 
+    #[inline]
     fn as_debuggable(&mut self) -> Option<&mut dyn Debuggable> {
         None
     }
 
+    #[inline]
     fn as_inspectable(&mut self) -> Option<&mut dyn Inspectable> {
         None
     }
@@ -201,12 +208,70 @@ pub fn wrap_transmutable<T: Transmutable + 'static>(value: T) -> TransmutableBox
     Rc::new(RefCell::new(Box::new(value)))
 }
 
+static NEXT_ID: AtomicUsize = AtomicUsize::new(1);
+
+#[derive(Copy, Clone, Debug)]
+pub struct DeviceId(usize);
+
+impl DeviceId {
+    pub fn new() -> Self {
+        let next = NEXT_ID.load(Ordering::Acquire);
+        NEXT_ID.store(next + 1, Ordering::Release);
+        Self(next)
+    }
+}
+
+impl Default for DeviceId {
+    fn default() -> Self {
+        Self::new()
+    }
+}
 
 #[derive(Clone)]
-pub struct Device(TransmutableBox);
+pub struct Device(DeviceId, TransmutableBox);
 
 impl Device {
+    pub fn new<T>(value: T) -> Self
+    where
+        T: Transmutable + 'static
+    {
+        Self(DeviceId::new(), wrap_transmutable(value))
+    }
 
+    pub fn borrow_mut(&self) -> RefMut<'_, Box<dyn Transmutable>> {
+        self.1.borrow_mut()
+    }
+
+    pub fn try_borrow_mut(&self) -> Result<RefMut<'_, Box<dyn Transmutable>>, BorrowMutError> {
+        self.1.try_borrow_mut()
+    }
+
+    /*
+    #[inline]
+    pub fn as_steppable(&mut self) -> Option<&mut dyn Steppable> {
+        self.1.borrow_mut().as_steppable()
+    }
+
+    #[inline]
+    pub fn as_addressable(&mut self) -> Option<&mut dyn Addressable> {
+        None
+    }
+
+    #[inline]
+    pub fn as_interruptable(&mut self) -> Option<&mut dyn Interruptable> {
+        None
+    }
+
+    #[inline]
+    pub fn as_debuggable(&mut self) -> Option<&mut dyn Debuggable> {
+        None
+    }
+
+    #[inline]
+    pub fn as_inspectable(&mut self) -> Option<&mut dyn Inspectable> {
+        None
+    }
+    */
 }
 
 
diff --git a/emulator/core/src/lib.rs b/emulator/core/src/lib.rs
index bf69dcf..e0500ea 100644
--- a/emulator/core/src/lib.rs
+++ b/emulator/core/src/lib.rs
@@ -16,7 +16,7 @@ pub use log::{trace, debug, info, warn, error};
 
 pub use crate::clock::{ClockTime, ClockDuration, Frequency};
 pub use crate::debugger::Debugger;
-pub use crate::devices::{Address, Addressable, Steppable, Interruptable, Debuggable, Inspectable, Transmutable, TransmutableBox};
+pub use crate::devices::{Address, Addressable, Steppable, Interruptable, Debuggable, Inspectable, Transmutable, TransmutableBox, Device};
 pub use crate::devices::{read_beu16, read_beu32, read_leu16, read_leu32, write_beu16, write_beu32, write_leu16, write_leu32, wrap_transmutable};
 pub use crate::error::{Error, ErrorType};
 pub use crate::interrupts::InterruptController;
diff --git a/emulator/core/src/memory.rs b/emulator/core/src/memory.rs
index d282d96..c327741 100644
--- a/emulator/core/src/memory.rs
+++ b/emulator/core/src/memory.rs
@@ -8,7 +8,7 @@ use std::fmt::Write;
 use crate::info;
 use crate::error::Error;
 use crate::clock::ClockTime;
-use crate::devices::{Address, Addressable, Transmutable, TransmutableBox, read_beu16};
+use crate::devices::{Address, Addressable, Transmutable, Device, read_beu16};
 
 
 pub struct MemoryBlock {
@@ -78,12 +78,12 @@ impl Transmutable for MemoryBlock {
 
 
 pub struct AddressRightShifter {
-    subdevice: TransmutableBox,
+    subdevice: Device,
     shift: u8,
 }
 
 impl AddressRightShifter {
-    pub fn new(subdevice: TransmutableBox, shift: u8) -> Self {
+    pub fn new(subdevice: Device, shift: u8) -> Self {
         Self {
             subdevice,
             shift,
@@ -114,12 +114,12 @@ impl Transmutable for AddressRightShifter {
 
 
 pub struct AddressRepeater {
-    subdevice: TransmutableBox,
+    subdevice: Device,
     range: Address,
 }
 
 impl AddressRepeater {
-    pub fn new(subdevice: TransmutableBox, range: Address) -> Self {
+    pub fn new(subdevice: Device, range: Address) -> Self {
         Self {
             subdevice,
             range,
@@ -154,7 +154,7 @@ impl Transmutable for AddressRepeater {
 pub struct Block {
     pub base: Address,
     pub size: usize,
-    pub dev: TransmutableBox,
+    pub dev: Device,
 }
 
 #[derive(Clone, Default)]
@@ -174,14 +174,14 @@ impl Bus {
         self.blocks.clear();
     }
 
-    pub fn insert(&mut self, base: Address, dev: TransmutableBox) {
+    pub fn insert(&mut self, base: Address, dev: Device) {
         let size = dev.borrow_mut().as_addressable().unwrap().size();
         let block = Block { base, size, dev };
         let i = self.blocks.iter().position(|cur| cur.base > block.base).unwrap_or(self.blocks.len());
         self.blocks.insert(i, block);
     }
 
-    pub fn get_device_at(&self, addr: Address, count: usize) -> Result<(TransmutableBox, Address), Error> {
+    pub fn get_device_at(&self, addr: Address, count: usize) -> Result<(Device, Address), Error> {
         for block in &self.blocks {
             if addr >= block.base && addr < (block.base + block.size as Address) {
                 let relative_addr = addr - block.base;
diff --git a/emulator/core/src/system.rs b/emulator/core/src/system.rs
index 1da0264..b971188 100644
--- a/emulator/core/src/system.rs
+++ b/emulator/core/src/system.rs
@@ -9,12 +9,12 @@ use crate::signals::EdgeSignal;
 use crate::error::{Error, ErrorType};
 use crate::interrupts::InterruptController;
 use crate::clock::{ClockTime, ClockDuration};
-use crate::devices::{Address, TransmutableBox};
+use crate::devices::{Address, Device};
 
 
 pub struct System {
     pub clock: ClockTime,
-    pub devices: HashMap<String, TransmutableBox>,
+    pub devices: HashMap<String, Device>,
     pub event_queue: Vec<NextStep>,
 
     pub debug_enabled: Cell<bool>,
@@ -55,28 +55,28 @@ impl System {
         self.interrupt_controller.borrow_mut()
     }
 
-    pub fn get_device(&self, name: &str) -> Result<TransmutableBox, Error> {
+    pub fn get_device(&self, name: &str) -> Result<Device, Error> {
         self.devices.get(name).cloned().ok_or_else(|| Error::new(&format!("system: no device named {}", name)))
     }
 
-    pub fn add_device(&mut self, name: &str, device: TransmutableBox) -> Result<(), Error> {
+    pub fn add_device(&mut self, name: &str, device: Device) -> Result<(), Error> {
         self.try_queue_device(device.clone());
         self.devices.insert(name.to_string(), device);
         Ok(())
     }
 
-    pub fn add_addressable_device(&mut self, addr: Address, device: TransmutableBox) -> Result<(), Error> {
+    pub fn add_addressable_device(&mut self, addr: Address, device: Device) -> Result<(), Error> {
         self.add_peripheral(&format!("mem{:x}", addr), addr, device)
     }
 
-    pub fn add_peripheral(&mut self, name: &str, addr: Address, device: TransmutableBox) -> Result<(), Error> {
+    pub fn add_peripheral(&mut self, name: &str, addr: Address, device: Device) -> Result<(), Error> {
         self.bus.borrow_mut().insert(addr, device.clone());
         self.try_queue_device(device.clone());
         self.devices.insert(name.to_string(), device);
         Ok(())
     }
 
-    pub fn add_interruptable_device(&mut self, name: &str, device: TransmutableBox) -> Result<(), Error> {
+    pub fn add_interruptable_device(&mut self, name: &str, device: Device) -> Result<(), Error> {
         self.try_queue_device(device.clone());
         self.devices.insert(name.to_string(), device);
         Ok(())
@@ -172,7 +172,7 @@ impl System {
         }
     }
 
-    fn try_queue_device(&mut self, device: TransmutableBox) {
+    fn try_queue_device(&mut self, device: Device) {
         if device.borrow_mut().as_steppable().is_some() {
             self.queue_device(NextStep::new(device));
         }
@@ -192,11 +192,11 @@ impl System {
 
 pub struct NextStep {
     pub next_clock: ClockTime,
-    pub device: TransmutableBox,
+    pub device: Device,
 }
 
 impl NextStep {
-    pub fn new(device: TransmutableBox) -> Self {
+    pub fn new(device: Device) -> Self {
         Self {
             next_clock: ClockTime::START,
             device,
diff --git a/emulator/frontends/minifb/src/lib.rs b/emulator/frontends/minifb/src/lib.rs
index 7bd478e..0b800b2 100644
--- a/emulator/frontends/minifb/src/lib.rs
+++ b/emulator/frontends/minifb/src/lib.rs
@@ -7,7 +7,7 @@ use std::time::{Duration, Instant};
 use minifb::{self, Key, MouseMode, MouseButton};
 use clap::{App, Arg, ArgMatches};
 
-use moa_core::{System, Error, ClockDuration, wrap_transmutable};
+use moa_core::{System, Error, ClockDuration, Device};
 use moa_core::host::{Host, Audio, KeyEvent, MouseEvent, MouseState, ControllerDevice, ControllerEvent, EventSender, PixelEncoding, Frame, FrameReceiver};
 
 use moa_common::{AudioMixer, AudioSource};
@@ -216,7 +216,7 @@ impl MiniFrontend {
 
         if self.mixer.borrow_mut().num_sources() != 0 && matches.occurrences_of("disable-audio") == 0 {
             if let Some(system) = system.as_mut() {
-                system.add_device("mixer", wrap_transmutable(self.mixer.clone())).unwrap();
+                system.add_device("mixer", Device::new(self.mixer.clone())).unwrap();
             }
             self.audio = Some(CpalAudioOutput::create_audio_output(self.mixer.borrow_mut().get_sink()));
         }
diff --git a/emulator/frontends/pixels/src/web.rs b/emulator/frontends/pixels/src/web.rs
index d3adc32..71802d8 100644
--- a/emulator/frontends/pixels/src/web.rs
+++ b/emulator/frontends/pixels/src/web.rs
@@ -12,7 +12,7 @@ use web_sys::Event;
 use wasm_bindgen::JsCast;
 use wasm_bindgen::closure::Closure;
 
-use moa_core::{ClockDuration, System, wrap_transmutable};
+use moa_core::{ClockDuration, System, Device};
 use moa_core::host::{ControllerInput, ControllerDevice, ControllerEvent, EventSender};
 
 use crate::settings;
@@ -130,7 +130,7 @@ pub fn load_system(handle: &mut HostHandle, load: LoadSystemFnHandle) -> SystemH
     let mut system = load.0(&mut handle.0, settings::get().rom_data.clone()).unwrap();
     let mixer = handle.0.get_mixer();
     if mixer.borrow_mut().num_sources() > 0 {
-        system.add_device("mixer", wrap_transmutable(mixer.clone())).unwrap();
+        system.add_device("mixer", Device::new(mixer.clone())).unwrap();
     }
     SystemHandle(system)
 }
diff --git a/emulator/systems/computie/src/system.rs b/emulator/systems/computie/src/system.rs
index 36ccf54..34180e1 100644
--- a/emulator/systems/computie/src/system.rs
+++ b/emulator/systems/computie/src/system.rs
@@ -1,5 +1,5 @@
 
-use moa_core::{System, Error, Frequency, Debuggable, MemoryBlock, BusPort, wrap_transmutable};
+use moa_core::{System, Error, Frequency, Debuggable, MemoryBlock, BusPort, Device};
 use moa_core::host::Host;
 
 use moa_m68k::{M68k, M68kType};
@@ -11,20 +11,20 @@ pub fn build_computie<H: Host>(host: &H) -> Result<System, Error> {
     let mut system = System::default();
 
     let monitor = MemoryBlock::load("binaries/computie/monitor.bin")?;
-    system.add_addressable_device(0x00000000, wrap_transmutable(monitor))?;
+    system.add_addressable_device(0x00000000, Device::new(monitor))?;
 
     let mut ram = MemoryBlock::new(vec![0; 0x00100000]);
     ram.load_at(0, "binaries/computie/kernel.bin")?;
-    system.add_addressable_device(0x00100000, wrap_transmutable(ram))?;
+    system.add_addressable_device(0x00100000, Device::new(ram))?;
 
     let mut ata = AtaDevice::default();
     ata.load("binaries/computie/disk-with-partition-table.img")?;
-    system.add_addressable_device(0x00600000, wrap_transmutable(ata))?;
+    system.add_addressable_device(0x00600000, Device::new(ata))?;
 
     let mut serial = MC68681::default();
     launch_terminal_emulator(serial.port_a.connect(host.add_pty()?)?);
     launch_slip_connection(serial.port_b.connect(host.add_pty()?)?);
-    system.add_addressable_device(0x00700000, wrap_transmutable(serial))?;
+    system.add_addressable_device(0x00700000, Device::new(serial))?;
 
 
     let mut cpu = M68k::new(M68kType::MC68010, Frequency::from_hz(10_000_000), BusPort::new(0, 24, 16, system.bus.clone()));
@@ -40,7 +40,7 @@ pub fn build_computie<H: Host>(host: &H) -> Result<System, Error> {
 
     cpu.add_breakpoint(0);
 
-    system.add_interruptable_device("cpu", wrap_transmutable(cpu))?;
+    system.add_interruptable_device("cpu", Device::new(cpu))?;
 
     Ok(system)
 }
@@ -49,20 +49,20 @@ pub fn build_computie_k30<H: Host>(host: &H) -> Result<System, Error> {
     let mut system = System::default();
 
     let monitor = MemoryBlock::load("binaries/computie/monitor-68030.bin")?;
-    system.add_addressable_device(0x00000000, wrap_transmutable(monitor))?;
+    system.add_addressable_device(0x00000000, Device::new(monitor))?;
 
     let mut ram = MemoryBlock::new(vec![0; 0x00100000]);
     ram.load_at(0, "binaries/computie/kernel-68030.bin")?;
-    system.add_addressable_device(0x00100000, wrap_transmutable(ram))?;
+    system.add_addressable_device(0x00100000, Device::new(ram))?;
 
     let mut ata = AtaDevice::default();
     ata.load("binaries/computie/disk-with-partition-table.img")?;
-    system.add_addressable_device(0x00600000, wrap_transmutable(ata))?;
+    system.add_addressable_device(0x00600000, Device::new(ata))?;
 
     let mut serial = MC68681::default();
     launch_terminal_emulator(serial.port_a.connect(host.add_pty()?)?);
     //launch_slip_connection(serial.port_b.connect(host.add_pty()?)?);
-    system.add_addressable_device(0x00700000, wrap_transmutable(serial))?;
+    system.add_addressable_device(0x00700000, Device::new(serial))?;
 
 
     let cpu = M68k::new(M68kType::MC68030, Frequency::from_hz(10_000_000), BusPort::new(0, 32, 32, system.bus.clone()));
@@ -76,7 +76,7 @@ pub fn build_computie_k30<H: Host>(host: &H) -> Result<System, Error> {
     //cpu.decoder.dump_disassembly(&mut system, 0x100000, 0x2000);
     //cpu.decoder.dump_disassembly(&mut system, 0x2ac, 0x200);
 
-    system.add_interruptable_device("cpu", wrap_transmutable(cpu))?;
+    system.add_interruptable_device("cpu", Device::new(cpu))?;
 
     Ok(system)
 }
diff --git a/emulator/systems/genesis/src/peripherals/ym7101.rs b/emulator/systems/genesis/src/peripherals/ym7101.rs
index ea76cfa..092d09c 100644
--- a/emulator/systems/genesis/src/peripherals/ym7101.rs
+++ b/emulator/systems/genesis/src/peripherals/ym7101.rs
@@ -1,6 +1,6 @@
 
 use moa_core::{debug, warn, error};
-use moa_core::{System, Error, EdgeSignal, ClockTime, ClockDuration, Frequency, Signal, Address, Addressable, Steppable, Inspectable, Transmutable, TransmutableBox, read_beu16, dump_slice};
+use moa_core::{System, Error, EdgeSignal, ClockTime, ClockDuration, Frequency, Signal, Address, Addressable, Steppable, Inspectable, Transmutable, Device, read_beu16, dump_slice};
 use moa_core::host::{self, Host, Pixel, PixelEncoding, Frame, FrameSender};
 
 
@@ -709,14 +709,14 @@ impl Steppable for Ym7101 {
 pub struct Ym7101 {
     sender: FrameSender,
     state: Ym7101State,
-    sn_sound: TransmutableBox,
+    sn_sound: Device,
 
     pub external_interrupt: Signal<bool>,
     pub frame_complete: EdgeSignal,
 }
 
 impl Ym7101 {
-    pub fn new<H: Host>(host: &mut H, external_interrupt: Signal<bool>, sn_sound: TransmutableBox) -> Ym7101 {
+    pub fn new<H: Host>(host: &mut H, external_interrupt: Signal<bool>, sn_sound: Device) -> Ym7101 {
         let (sender, receiver) = host::frame_queue(320, 224);
         host.add_video_source(receiver).unwrap();
 
diff --git a/emulator/systems/genesis/src/system.rs b/emulator/systems/genesis/src/system.rs
index c79dc61..09096aa 100644
--- a/emulator/systems/genesis/src/system.rs
+++ b/emulator/systems/genesis/src/system.rs
@@ -3,7 +3,7 @@ use std::mem;
 use std::rc::Rc;
 use std::cell::RefCell;
 
-use moa_core::{System, Error, Frequency, Signal, MemoryBlock, Bus, BusPort, Address, Addressable, Debuggable, wrap_transmutable};
+use moa_core::{System, Error, Frequency, Signal, MemoryBlock, Bus, BusPort, Address, Addressable, Debuggable, Device};
 use moa_core::host::Host;
 
 use moa_m68k::{M68k, M68kType};
@@ -58,22 +58,22 @@ pub fn build_genesis<H: Host>(host: &mut H, mut options: SegaGenesisOptions) ->
     //let mut rom = MemoryBlock::load("binaries/genesis/Teenage Mutant Ninja Turtles - The Hyperstone Heist (U) [!].bin").unwrap();
     //rom.read_only();
     let rom_end = rom.size();
-    system.add_addressable_device(0x00000000, wrap_transmutable(rom)).unwrap();
+    system.add_addressable_device(0x00000000, Device::new(rom)).unwrap();
 
     let cartridge_nvram = MemoryBlock::new(vec![0; 0x400000 - rom_end]);
-    system.add_addressable_device(rom_end as Address, wrap_transmutable(cartridge_nvram)).unwrap();
+    system.add_addressable_device(rom_end as Address, Device::new(cartridge_nvram)).unwrap();
 
     let ram = MemoryBlock::new(vec![0; 0x00010000]);
-    system.add_addressable_device(0x00ff0000, wrap_transmutable(ram)).unwrap();
+    system.add_addressable_device(0x00ff0000, Device::new(ram)).unwrap();
 
 
     // Build the Coprocessor's Bus
     let bank_register = Signal::new(0);
-    let coproc_ram = wrap_transmutable(MemoryBlock::new(vec![0; 0x00002000]));
-    let coproc_ym_sound = wrap_transmutable(Ym2612::new(host, Frequency::from_hz(7_670_454))?);
-    let coproc_sn_sound = wrap_transmutable(Sn76489::new(host, Frequency::from_hz(3_579_545))?);
-    let coproc_register = wrap_transmutable(CoprocessorBankRegister::new(bank_register.clone()));
-    let coproc_area = wrap_transmutable(CoprocessorBankArea::new(bank_register, system.bus.clone()));
+    let coproc_ram = Device::new(MemoryBlock::new(vec![0; 0x00002000]));
+    let coproc_ym_sound = Device::new(Ym2612::new(host, Frequency::from_hz(7_670_454))?);
+    let coproc_sn_sound = Device::new(Sn76489::new(host, Frequency::from_hz(3_579_545))?);
+    let coproc_register = Device::new(CoprocessorBankRegister::new(bank_register.clone()));
+    let coproc_area = Device::new(CoprocessorBankArea::new(bank_register, system.bus.clone()));
 
     let coproc_bus = Rc::new(RefCell::new(Bus::default()));
     coproc_bus.borrow_mut().set_ignore_unmapped(true);
@@ -95,22 +95,22 @@ pub fn build_genesis<H: Host>(host: &mut H, mut options: SegaGenesisOptions) ->
     system.add_addressable_device(0x00a06000, coproc_register)?;
     //system.add_addressable_device(0x00c00010, coproc_sn_sound)?;
     system.add_device("sn_sound", coproc_sn_sound.clone())?;
-    system.add_device("coproc", wrap_transmutable(coproc))?;
+    system.add_device("coproc", Device::new(coproc))?;
 
 
     let controllers = GenesisControllers::new(host)?;
     let interrupt = controllers.get_interrupt_signal();
-    system.add_addressable_device(0x00a10000, wrap_transmutable(controllers)).unwrap();
+    system.add_addressable_device(0x00a10000, Device::new(controllers)).unwrap();
 
     let coproc = CoprocessorCoordinator::new(reset, bus_request);
-    system.add_addressable_device(0x00a11000, wrap_transmutable(coproc)).unwrap();
+    system.add_addressable_device(0x00a11000, Device::new(coproc)).unwrap();
 
     let vdp = Ym7101::new(host, interrupt, coproc_sn_sound);
     system.break_signal = Some(vdp.frame_complete.clone());
-    system.add_peripheral("vdp", 0x00c00000, wrap_transmutable(vdp)).unwrap();
+    system.add_peripheral("vdp", 0x00c00000, Device::new(vdp)).unwrap();
 
     let cpu = M68k::new(M68kType::MC68000, Frequency::from_hz(7_670_454), BusPort::new(0, 24, 16, system.bus.clone()));
-    system.add_interruptable_device("cpu", wrap_transmutable(cpu)).unwrap();
+    system.add_interruptable_device("cpu", Device::new(cpu)).unwrap();
 
     Ok(system)
 }
diff --git a/emulator/systems/macintosh/src/peripherals/mainboard.rs b/emulator/systems/macintosh/src/peripherals/mainboard.rs
index 2988bdb..3e2c641 100644
--- a/emulator/systems/macintosh/src/peripherals/mainboard.rs
+++ b/emulator/systems/macintosh/src/peripherals/mainboard.rs
@@ -2,7 +2,7 @@
 use std::rc::Rc;
 use std::cell::RefCell;
 
-use moa_core::{System, Bus, Error, Observable, ClockTime, ClockDuration, Address, Addressable, AddressRepeater, Steppable, Transmutable, TransmutableBox, wrap_transmutable};
+use moa_core::{System, Bus, Error, Observable, ClockTime, ClockDuration, Address, Addressable, AddressRepeater, Steppable, Transmutable, Device};
 
 use moa_peripherals_mos::Mos6522;
 use moa_peripherals_zilog::Z8530;
@@ -22,7 +22,7 @@ pub struct Mainboard {
 }
 
 impl Mainboard {
-    pub fn new(ram: TransmutableBox, rom: TransmutableBox) -> Result<Self, Error> {
+    pub fn new(ram: Device, rom: Device) -> Result<Self, Error> {
         let scc1 = Z8530::default();
         let scc2 = Z8530::default();
         let iwm = IWM::default();
@@ -45,16 +45,16 @@ impl Mainboard {
             if (port.data & 0x10) == 0 {
                 println!("{}: overlay is 0 (normal)", DEV_NAME);
                 lower_bus.borrow_mut().clear_all_bus_devices();
-                lower_bus.borrow_mut().insert(0x000000, wrap_transmutable(AddressRepeater::new(ram.clone(), 0x400000)));
-                lower_bus.borrow_mut().insert(0x400000, wrap_transmutable(AddressRepeater::new(rom.clone(), 0x100000)));
-                lower_bus.borrow_mut().insert(0x600000, wrap_transmutable(AddressRepeater::new(rom.clone(), 0x100000)));
+                lower_bus.borrow_mut().insert(0x000000, Device::new(AddressRepeater::new(ram.clone(), 0x400000)));
+                lower_bus.borrow_mut().insert(0x400000, Device::new(AddressRepeater::new(rom.clone(), 0x100000)));
+                lower_bus.borrow_mut().insert(0x600000, Device::new(AddressRepeater::new(rom.clone(), 0x100000)));
             } else {
                 println!("{}: overlay is 1 (startup)", DEV_NAME);
                 lower_bus.borrow_mut().clear_all_bus_devices();
-                lower_bus.borrow_mut().insert(0x000000, wrap_transmutable(AddressRepeater::new(rom.clone(), 0x100000)));
-                lower_bus.borrow_mut().insert(0x200000, wrap_transmutable(AddressRepeater::new(rom.clone(), 0x100000)));
-                lower_bus.borrow_mut().insert(0x400000, wrap_transmutable(AddressRepeater::new(rom.clone(), 0x100000)));
-                lower_bus.borrow_mut().insert(0x600000, wrap_transmutable(AddressRepeater::new(ram.clone(), 0x200000)));
+                lower_bus.borrow_mut().insert(0x000000, Device::new(AddressRepeater::new(rom.clone(), 0x100000)));
+                lower_bus.borrow_mut().insert(0x200000, Device::new(AddressRepeater::new(rom.clone(), 0x100000)));
+                lower_bus.borrow_mut().insert(0x400000, Device::new(AddressRepeater::new(rom.clone(), 0x100000)));
+                lower_bus.borrow_mut().insert(0x600000, Device::new(AddressRepeater::new(ram.clone(), 0x200000)));
             }
         });
 
diff --git a/emulator/systems/macintosh/src/system.rs b/emulator/systems/macintosh/src/system.rs
index bfb77be..84f1091 100644
--- a/emulator/systems/macintosh/src/system.rs
+++ b/emulator/systems/macintosh/src/system.rs
@@ -1,5 +1,5 @@
 
-use moa_core::{System, Error, Frequency, MemoryBlock, BusPort, Debuggable, wrap_transmutable};
+use moa_core::{System, Error, Frequency, MemoryBlock, BusPort, Debuggable, Device};
 use moa_core::host::Host;
 
 use moa_m68k::{M68k, M68kType};
@@ -63,10 +63,10 @@ pub fn build_macintosh_512k<H: Host>(host: &mut H) -> Result<System, Error> {
     rom.read_only();
 
     let video = MacVideo::new(host)?;
-    system.add_device("video", wrap_transmutable(video)).unwrap();
+    system.add_device("video", Device::new(video)).unwrap();
 
-    let mainboard = Mainboard::new(wrap_transmutable(ram), wrap_transmutable(rom))?;
-    system.add_addressable_device(0x00000000, wrap_transmutable(mainboard))?;
+    let mainboard = Mainboard::new(Device::new(ram), Device::new(rom))?;
+    system.add_addressable_device(0x00000000, Device::new(mainboard))?;
 
 
     let mut cpu = M68k::new(M68kType::MC68000, Frequency::from_hz(7_833_600), BusPort::new(0, 24, 16, system.bus.clone()));
@@ -121,7 +121,7 @@ pub fn build_macintosh_512k<H: Host>(host: &mut H) -> Result<System, Error> {
     panic!("");
     */
 
-    system.add_interruptable_device("cpu", wrap_transmutable(cpu))?;
+    system.add_interruptable_device("cpu", Device::new(cpu))?;
 
     Ok(system)
 }
diff --git a/emulator/systems/trs80/src/system.rs b/emulator/systems/trs80/src/system.rs
index 99182c4..1359666 100644
--- a/emulator/systems/trs80/src/system.rs
+++ b/emulator/systems/trs80/src/system.rs
@@ -1,5 +1,5 @@
 
-use moa_core::{System, Error, Frequency, MemoryBlock, BusPort, wrap_transmutable};
+use moa_core::{System, Error, Frequency, MemoryBlock, BusPort, Device};
 use moa_core::host::Host;
 
 use moa_z80::{Z80, Z80Type};
@@ -32,15 +32,15 @@ pub fn build_trs80<H: Host>(host: &mut H, options: Trs80Options) -> Result<Syste
     //rom.load_at(0x0000, "binaries/trs80/level2.rom")?;
     rom.load_at(0x0000, &options.rom)?;
     rom.read_only();
-    system.add_addressable_device(0x0000, wrap_transmutable(rom))?;
+    system.add_addressable_device(0x0000, Device::new(rom))?;
 
     let ram = MemoryBlock::new(vec![0; options.memory as usize]);
-    system.add_addressable_device(0x4000, wrap_transmutable(ram))?;
+    system.add_addressable_device(0x4000, Device::new(ram))?;
 
     let keyboard = Model1Keyboard::new(host)?;
-    system.add_addressable_device(0x37E0, wrap_transmutable(keyboard)).unwrap();
+    system.add_addressable_device(0x37E0, Device::new(keyboard)).unwrap();
     let video = Model1Video::new(host)?;
-    system.add_addressable_device(0x37E0 + 0x420, wrap_transmutable(video)).unwrap();
+    system.add_addressable_device(0x37E0 + 0x420, Device::new(video)).unwrap();
 
     // TODO the ioport needs to be hooked up
     let cpu = Z80::new(Z80Type::Z80, options.frequency, BusPort::new(0, 16, 8, system.bus.clone()), None);
@@ -68,7 +68,7 @@ pub fn build_trs80<H: Host>(host: &mut H, options: Trs80Options) -> Result<Syste
     //cpu.add_breakpoint(0x9e2);
     //cpu.add_breakpoint(0x9f9);
 
-    system.add_interruptable_device("cpu", wrap_transmutable(cpu))?;
+    system.add_interruptable_device("cpu", Device::new(cpu))?;
 
     Ok(system)
 }