diff --git a/src/bus.rs b/src/bus.rs
new file mode 100644
index 0000000..4a57ddf
--- /dev/null
+++ b/src/bus.rs
@@ -0,0 +1,166 @@
+// bus.rs
+
+use crate::{Memory, Mouse};
+
+use std::convert::TryInto;
+use std::io::{stdout, Write};
+use std::sync::{Arc, Mutex};
+use std::thread;
+
+use rodio::{OutputStream, buffer::SamplesBuffer, Sink};
+
+pub struct Bus {
+    pub memory: Memory,
+    pub mouse: Arc<Mutex<Mouse>>,
+}
+
+impl Bus {
+    pub fn read_io(&mut self, port: u32) -> u32 {
+        match port {
+            0x02000000..=0x0200031F => { // overlay port
+                let overlay_lock = self.memory.overlays.lock().unwrap();
+                let overlay_number = (port & 0x000000FF) as usize;
+                let setting = (port & 0x0000FF00) >> 8;
+
+                match setting {
+                    0x00 => {
+                        // we're reading the position of this overlay
+                        let x = overlay_lock[overlay_number].x as u32;
+                        let y = overlay_lock[overlay_number].y as u32;
+                        (y << 16) | x
+                    }
+                    0x01 => {
+                        // we're reading the size of this overlay
+                        let width = overlay_lock[overlay_number].width as u32;
+                        let height = overlay_lock[overlay_number].height as u32;
+                        (height << 16) | width
+                    }
+                    0x02 => {
+                        // we're reading the framebuffer pointer of this overlay
+                        overlay_lock[overlay_number].framebuffer_pointer + 0x02000000
+                    }
+                    0x03 => {
+                        // we're reading the enable status of this overlay
+                        overlay_lock[overlay_number].enabled as u32
+                    }
+                    _ => panic!("invalid overlay control port"),
+                }
+            }
+            0x02000400..=0x02000401 => { // mouse port
+                let setting = (port & 0x000000FF) as u8;
+                match setting {
+                    0x00 => {
+                        // we're reading the button states
+                        let mut byte: u8 = 0x00;
+                        let mut mouse_lock = self.mouse.lock().expect("failed to lock the mouse mutex");
+                        if mouse_lock.click {
+                            byte |= 0b01;
+                            mouse_lock.click = false;
+                        }
+                        if mouse_lock.held {
+                            byte |= 0b10;
+                        } else {
+                            byte &= !0b10;
+                        }
+                        byte as u32
+                    }
+                    0x01 => {
+                        // we're reading the position
+                        let mouse_lock = self.mouse.lock().expect("failed to lock the mouse mutex");
+                        let x = mouse_lock.x as u32;
+                        let y = mouse_lock.y as u32;
+                        (y << 16) | x
+                    }
+                    _ => panic!("invalid mouse control port"),
+                }
+            }
+            _ => 0,
+        }
+    }
+    pub fn write_io(&mut self, port: u32, word: u32) {
+        match port {
+            0x00000000 => { // terminal output port
+                print!("{}", word as u8 as char);
+                stdout().flush().expect("could not flush stdout");
+            }
+            0x02000000..=0x0200031F => { // overlay port
+                let mut overlay_lock = self.memory.overlays.lock().unwrap();
+                let overlay_number = (port & 0x000000FF) as usize;
+                let setting = (port & 0x0000FF00) >> 8;
+
+                match setting {
+                    0x00 => {
+                        // we're setting the position of this overlay
+                        let x = (word & 0x0000FFFF) as usize;
+                        let y = ((word & 0xFFFF0000) >> 16) as usize;
+                        overlay_lock[overlay_number].x = x;
+                        overlay_lock[overlay_number].y = y;
+                    }
+                    0x01 => {
+                        // we're setting the size of this overlay
+                        let width = (word & 0x0000FFFF) as usize;
+                        let height = ((word & 0xFFFF0000) >> 16) as usize;
+                        overlay_lock[overlay_number].width = width;
+                        overlay_lock[overlay_number].height = height;
+                    }
+                    0x02 => {
+                        // we're setting the framebuffer pointer of this overlay
+                        if word < 0x02000000 {
+                            panic!("overlay framebuffer must be within shared memory");
+                        }
+                        overlay_lock[overlay_number].framebuffer_pointer = word - 0x02000000;
+                    }
+                    0x03 => {
+                        // we're setting the enable status of this overlay
+                        overlay_lock[overlay_number].enabled = word != 0;
+                    }
+                    _ => panic!("invalid overlay control port"),
+                }
+            }
+            0x02000320 => { // audio port
+                if word < 0x02000000 {
+                    panic!("audio buffer must be within shared memory");
+                }
+                let address = word as usize - 0x02000000;
+                let shared_memory_lock = self.memory.shared_memory.lock().unwrap();
+
+                let length = u32::from_le_bytes(shared_memory_lock[address..address+4].try_into().unwrap()) as usize;
+                let start_address = address + 4;
+                let end_address = start_address + length;
+
+                let audio_data: Vec<i16> = shared_memory_lock[start_address..end_address].to_vec().chunks_exact(2).map(|x| ((x[1] as i16) << 8) | x[0] as i16).collect();
+                let builder = thread::Builder::new().name("audio".to_string());
+                builder.spawn({
+                    move || {
+                        let buffer = SamplesBuffer::new(1, 44100, audio_data);
+                        let (_stream, stream_handle) = OutputStream::try_default().unwrap();
+                        let sink = Sink::try_new(&stream_handle).unwrap();
+                        sink.append(buffer);
+                        sink.sleep_until_end();
+                    }
+                }).unwrap();
+            }
+            0x02000400..=0x02000401 => { // mouse port
+                let setting = (port & 0x000000FF) as u8;
+                match setting {
+                    0x00 => {
+                        // we're setting the button states
+                        let mut mouse_lock = self.mouse.lock().expect("failed to lock the mouse mutex");
+                        mouse_lock.click = word & (1 << 0) != 0;
+                        mouse_lock.held = word & (1 << 1) != 0;
+                    }
+                    0x01 => {
+                        // we're setting the position
+                        let mut mouse_lock = self.mouse.lock().expect("failed to lock the mouse mutex");
+                        let x = (word & 0x0000FFFF) as u16;
+                        let y = ((word & 0xFFFF0000) >> 16) as u16;
+                        mouse_lock.x = x;
+                        mouse_lock.y = y;
+                    }
+                    _ => panic!("invalid mouse control port"),
+                }
+            }
+            _ => return,
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/cpu.rs b/src/cpu.rs
index 1bab26b..d40ea12 100644
--- a/src/cpu.rs
+++ b/src/cpu.rs
@@ -3,7 +3,7 @@
 // TODO: in the instruction match statement, all of the register ones have `let result` inside the if statement
 //       move this up to match all of the other ones (or move all of the other ones down, which would probably be better anyways)
 
-use crate::{Mouse, Overlay};
+use crate::{Bus, Overlay};
 use std::sync::{Arc, Mutex};
 
 const DEBUG: bool = false;
@@ -95,24 +95,6 @@ impl Memory {
     }
 }
 
-pub trait IO {
-    // called during the `in` instruction
-    // default implementation returns 0
-    fn read_io(&mut self, port: u32) -> u32 {
-        if DEBUG { println!("read_io(): port: {:#010X}", port); }
-        0
-    }
-    // called during the `out` instruction
-    fn write_io(&mut self, port: u32, word: u32) {
-        if DEBUG { println!("write_io(): port: {:#010X}, word: {:#010X}", port, word); }
-    }
-}
-
-pub struct Bus {
-    pub memory: Memory,
-    pub mouse: Arc<Mutex<Mouse>>,
-}
-
 #[derive(Copy, Clone)]
 pub struct Flag {
     pub carry: bool,
diff --git a/src/main.rs b/src/main.rs
index fbadb4e..d00cc47 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,16 +1,16 @@
 // main.rs
 
+pub mod bus;
 pub mod cpu;
 pub mod mouse;
-use cpu::{Bus, Cpu, Memory, Interrupt, IO};
+use bus::Bus;
+use cpu::{Cpu, Memory, Interrupt};
 use mouse::Mouse;
 
-use std::convert::TryInto;
 use std::env;
 use std::fs::read;
 //use std::process::exit;
 use std::sync::{Arc, mpsc, Mutex};
-use std::io::{stdout, Write};
 use std::thread;
 
 use log::error;
@@ -21,8 +21,6 @@ use winit::event_loop::{ControlFlow, EventLoop};
 use winit::window::WindowBuilder;
 use winit_input_helper::WinitInputHelper;
 
-use rodio::{OutputStream, buffer::SamplesBuffer, Sink};
-
 const WIDTH: usize = 640;
 const HEIGHT: usize = 480;
 
@@ -41,157 +39,6 @@ pub struct Overlay {
     framebuffer_pointer: u32,
 }
 
-impl IO for Bus {
-    fn read_io(&mut self, port: u32) -> u32 {
-        match port {
-            0x02000000..=0x0200031F => { // overlay port
-                let overlay_lock = self.memory.overlays.lock().unwrap();
-                let overlay_number = (port & 0x000000FF) as usize;
-                let setting = (port & 0x0000FF00) >> 8;
-
-                match setting {
-                    0x00 => {
-                        // we're reading the position of this overlay
-                        let x = overlay_lock[overlay_number].x as u32;
-                        let y = overlay_lock[overlay_number].y as u32;
-                        (y << 16) | x
-                    }
-                    0x01 => {
-                        // we're reading the size of this overlay
-                        let width = overlay_lock[overlay_number].width as u32;
-                        let height = overlay_lock[overlay_number].height as u32;
-                        (height << 16) | width
-                    }
-                    0x02 => {
-                        // we're reading the framebuffer pointer of this overlay
-                        overlay_lock[overlay_number].framebuffer_pointer + 0x02000000
-                    }
-                    0x03 => {
-                        // we're reading the enable status of this overlay
-                        overlay_lock[overlay_number].enabled as u32
-                    }
-                    _ => panic!("invalid overlay control port"),
-                }
-            }
-            0x02000400..=0x02000401 => { // mouse port
-                let setting = (port & 0x000000FF) as u8;
-                match setting {
-                    0x00 => {
-                        // we're reading the button states
-                        let mut byte: u8 = 0x00;
-                        let mut mouse_lock = self.mouse.lock().expect("failed to lock the mouse mutex");
-                        if mouse_lock.click {
-                            byte |= 0b01;
-                            mouse_lock.click = false;
-                        }
-                        if mouse_lock.held {
-                            byte |= 0b10;
-                        } else {
-                            byte &= !0b10;
-                        }
-                        byte as u32
-                    }
-                    0x01 => {
-                        // we're reading the position
-                        let mouse_lock = self.mouse.lock().expect("failed to lock the mouse mutex");
-                        let x = mouse_lock.x as u32;
-                        let y = mouse_lock.y as u32;
-                        (y << 16) | x
-                    }
-                    _ => panic!("invalid mouse control port"),
-                }
-            }
-            _ => 0,
-        }
-    }
-    fn write_io(&mut self, port: u32, word: u32) {
-        match port {
-            0x00000000 => { // terminal output port
-                print!("{}", word as u8 as char);
-                stdout().flush().expect("could not flush stdout");
-            }
-            0x02000000..=0x0200031F => { // overlay port
-                let mut overlay_lock = self.memory.overlays.lock().unwrap();
-                let overlay_number = (port & 0x000000FF) as usize;
-                let setting = (port & 0x0000FF00) >> 8;
-
-                match setting {
-                    0x00 => {
-                        // we're setting the position of this overlay
-                        let x = (word & 0x0000FFFF) as usize;
-                        let y = ((word & 0xFFFF0000) >> 16) as usize;
-                        overlay_lock[overlay_number].x = x;
-                        overlay_lock[overlay_number].y = y;
-                    }
-                    0x01 => {
-                        // we're setting the size of this overlay
-                        let width = (word & 0x0000FFFF) as usize;
-                        let height = ((word & 0xFFFF0000) >> 16) as usize;
-                        overlay_lock[overlay_number].width = width;
-                        overlay_lock[overlay_number].height = height;
-                    }
-                    0x02 => {
-                        // we're setting the framebuffer pointer of this overlay
-                        if word < 0x02000000 {
-                            panic!("overlay framebuffer must be within shared memory");
-                        }
-                        overlay_lock[overlay_number].framebuffer_pointer = word - 0x02000000;
-                    }
-                    0x03 => {
-                        // we're setting the enable status of this overlay
-                        overlay_lock[overlay_number].enabled = word != 0;
-                    }
-                    _ => panic!("invalid overlay control port"),
-                }
-            }
-            0x02000320 => { // audio port
-                if word < 0x02000000 {
-                    panic!("audio buffer must be within shared memory");
-                }
-                let address = word as usize - 0x02000000;
-                let shared_memory_lock = self.memory.shared_memory.lock().unwrap();
-
-                let length = u32::from_le_bytes(shared_memory_lock[address..address+4].try_into().unwrap()) as usize;
-                let start_address = address + 4;
-                let end_address = start_address + length;
-
-                let audio_data: Vec<i16> = shared_memory_lock[start_address..end_address].to_vec().chunks_exact(2).map(|x| ((x[1] as i16) << 8) | x[0] as i16).collect();
-                let builder = thread::Builder::new().name("audio".to_string());
-                builder.spawn({
-                    move || {
-                        let buffer = SamplesBuffer::new(1, 44100, audio_data);
-                        let (_stream, stream_handle) = OutputStream::try_default().unwrap();
-                        let sink = Sink::try_new(&stream_handle).unwrap();
-                        sink.append(buffer);
-                        sink.sleep_until_end();
-                    }
-                }).unwrap();
-            }
-            0x02000400..=0x02000401 => { // mouse port
-                let setting = (port & 0x000000FF) as u8;
-                match setting {
-                    0x00 => {
-                        // we're setting the button states
-                        let mut mouse_lock = self.mouse.lock().expect("failed to lock the mouse mutex");
-                        mouse_lock.click = word & (1 << 0) != 0;
-                        mouse_lock.held = word & (1 << 1) != 0;
-                    }
-                    0x01 => {
-                        // we're setting the position
-                        let mut mouse_lock = self.mouse.lock().expect("failed to lock the mouse mutex");
-                        let x = (word & 0x0000FFFF) as u16;
-                        let y = ((word & 0xFFFF0000) >> 16) as u16;
-                        mouse_lock.x = x;
-                        mouse_lock.y = y;
-                    }
-                    _ => panic!("invalid mouse control port"),
-                }
-            }
-            _ => return,
-        }
-    }
-}
-
 fn main() {
     let args: Vec<String> = env::args().collect();
     /*if args.len() != 2 {