diff --git a/Machines/Vic-20/Vic20.cpp b/Machines/Vic-20/Vic20.cpp
new file mode 100644
index 000000000..58e027eaf
--- /dev/null
+++ b/Machines/Vic-20/Vic20.cpp
@@ -0,0 +1,9 @@
+//
+//  Vic20.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 04/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#include "Vic20.hpp"
diff --git a/Machines/Vic-20/Vic20.hpp b/Machines/Vic-20/Vic20.hpp
new file mode 100644
index 000000000..59f16351a
--- /dev/null
+++ b/Machines/Vic-20/Vic20.hpp
@@ -0,0 +1,22 @@
+//
+//  Vic20.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 04/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#ifndef Vic20_hpp
+#define Vic20_hpp
+
+#include "../../Processors/6502/CPU6502.hpp"
+#include "../CRTMachine.hpp"
+
+namespace Vic20 {
+
+class Machine: public CPU6502::Processor<Machine>, public CRTMachine::Machine {
+};
+
+}
+
+#endif /* Vic20_hpp */
diff --git a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj
index 0edc27528..375490caa 100644
--- a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj	
+++ b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj	
@@ -28,6 +28,10 @@
 		4B69FB3D1C4D908A00B5F0AA /* Tape.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B69FB3B1C4D908A00B5F0AA /* Tape.cpp */; };
 		4B69FB441C4D941400B5F0AA /* TapeUEF.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B69FB421C4D941400B5F0AA /* TapeUEF.cpp */; };
 		4B69FB461C4D950F00B5F0AA /* libz.tbd in Frameworks */ = {isa = PBXBuildFile; fileRef = 4B69FB451C4D950F00B5F0AA /* libz.tbd */; };
+		4B73C71A1D036BD90074D992 /* Vic20Document.swift in Sources */ = {isa = PBXBuildFile; fileRef = 4B73C7191D036BD90074D992 /* Vic20Document.swift */; };
+		4B73C71D1D036C030074D992 /* Vic20Document.xib in Resources */ = {isa = PBXBuildFile; fileRef = 4B73C71B1D036C030074D992 /* Vic20Document.xib */; };
+		4B886FF21D03B517004291C3 /* Vic20.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B886FF01D03B517004291C3 /* Vic20.cpp */; };
+		4B886FF51D03B61E004291C3 /* CSVic20.m in Sources */ = {isa = PBXBuildFile; fileRef = 4B886FF41D03B61E004291C3 /* CSVic20.m */; };
 		4B92EACA1B7C112B00246143 /* TimingTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 4B92EAC91B7C112B00246143 /* TimingTests.swift */; };
 		4BB298EE1B587D8400A49093 /* 6502_functional_test.bin in Resources */ = {isa = PBXBuildFile; fileRef = 4BB297E01B587D8300A49093 /* 6502_functional_test.bin */; };
 		4BB298EF1B587D8400A49093 /* AllSuiteA.bin in Resources */ = {isa = PBXBuildFile; fileRef = 4BB297E11B587D8300A49093 /* AllSuiteA.bin */; };
@@ -373,6 +377,12 @@
 		4B69FB421C4D941400B5F0AA /* TapeUEF.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = TapeUEF.cpp; sourceTree = "<group>"; };
 		4B69FB431C4D941400B5F0AA /* TapeUEF.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = TapeUEF.hpp; sourceTree = "<group>"; };
 		4B69FB451C4D950F00B5F0AA /* libz.tbd */ = {isa = PBXFileReference; lastKnownFileType = "sourcecode.text-based-dylib-definition"; name = libz.tbd; path = usr/lib/libz.tbd; sourceTree = SDKROOT; };
+		4B73C7191D036BD90074D992 /* Vic20Document.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Vic20Document.swift; sourceTree = "<group>"; };
+		4B73C71C1D036C030074D992 /* Base */ = {isa = PBXFileReference; lastKnownFileType = file.xib; name = Base; path = "Clock Signal/Base.lproj/Vic20Document.xib"; sourceTree = SOURCE_ROOT; };
+		4B886FF01D03B517004291C3 /* Vic20.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = Vic20.cpp; path = "Vic-20/Vic20.cpp"; sourceTree = "<group>"; };
+		4B886FF11D03B517004291C3 /* Vic20.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; name = Vic20.hpp; path = "Vic-20/Vic20.hpp"; sourceTree = "<group>"; };
+		4B886FF31D03B61E004291C3 /* CSVic20.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = CSVic20.h; sourceTree = "<group>"; };
+		4B886FF41D03B61E004291C3 /* CSVic20.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = CSVic20.m; sourceTree = "<group>"; };
 		4B92EAC91B7C112B00246143 /* TimingTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = TimingTests.swift; sourceTree = "<group>"; };
 		4BAE587D1C447B7A005B9AF0 /* KeyCodes.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = KeyCodes.h; sourceTree = "<group>"; };
 		4BB297DF1B587D8200A49093 /* Clock SignalTests-Bridging-Header.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "Clock SignalTests-Bridging-Header.h"; sourceTree = "<group>"; };
@@ -793,6 +803,8 @@
 				4B55CE4C1C3B3BDA0093A61B /* CSMachine.h */,
 				4B55CE4D1C3B3BDA0093A61B /* CSMachine.mm */,
 				4B55CE4F1C3B78A80093A61B /* CSMachine+Subclassing.h */,
+				4B886FF31D03B61E004291C3 /* CSVic20.h */,
+				4B886FF41D03B61E004291C3 /* CSVic20.m */,
 				4BAE587D1C447B7A005B9AF0 /* KeyCodes.h */,
 			);
 			path = Wrappers;
@@ -806,6 +818,8 @@
 				4B55CE571C3B7D360093A61B /* ElectronDocument.swift */,
 				4B2E2D931C399D1200138695 /* ElectronDocument.xib */,
 				4B55CE5E1C3B7D960093A61B /* MachineDocument.swift */,
+				4B73C7191D036BD90074D992 /* Vic20Document.swift */,
+				4B73C71B1D036C030074D992 /* Vic20Document.xib */,
 			);
 			path = Documents;
 			sourceTree = "<group>";
@@ -848,6 +862,15 @@
 			path = Formats;
 			sourceTree = "<group>";
 		};
+		4B886FF61D03B632004291C3 /* Vic-20 */ = {
+			isa = PBXGroup;
+			children = (
+				4B886FF01D03B517004291C3 /* Vic20.cpp */,
+				4B886FF11D03B517004291C3 /* Vic20.hpp */,
+			);
+			name = "Vic-20";
+			sourceTree = "<group>";
+		};
 		4BB297E41B587D8300A49093 /* Wolfgang Lorenz 6502 test suite */ = {
 			isa = PBXGroup;
 			children = (
@@ -1191,9 +1214,10 @@
 		4BB73EDC1B587CA500552FC2 /* Machines */ = {
 			isa = PBXGroup;
 			children = (
+				4B046DC31CFE651500E9E45E /* CRTMachine.hpp */,
 				4B2E2D961C3A06EC00138695 /* Atari2600 */,
 				4B2E2D9E1C3A070900138695 /* Electron */,
-				4B046DC31CFE651500E9E45E /* CRTMachine.hpp */,
+				4B886FF61D03B632004291C3 /* Vic-20 */,
 			);
 			name = Machines;
 			path = ../../Machines;
@@ -1370,6 +1394,7 @@
 				4BE5F85F1C3E1C2500C43F01 /* os.rom in Resources */,
 				4BCB70B41C947DDC005B1712 /* plus1.rom in Resources */,
 				4BB73EA71B587A5100552FC2 /* Atari2600Document.xib in Resources */,
+				4B73C71D1D036C030074D992 /* Vic20Document.xib in Resources */,
 				4BB73EAC1B587A5100552FC2 /* MainMenu.xib in Resources */,
 				4BE5F85E1C3E1C2500C43F01 /* basic.rom in Resources */,
 			);
@@ -1667,11 +1692,14 @@
 				4B55CE541C3B7ABF0093A61B /* CSElectron.mm in Sources */,
 				4B0CCC451C62D0B3001CAC5F /* CRT.cpp in Sources */,
 				4B55CE591C3B7D360093A61B /* ElectronDocument.swift in Sources */,
+				4B886FF21D03B517004291C3 /* Vic20.cpp in Sources */,
 				4BC3B74F1CD194CC00F86E85 /* Shader.cpp in Sources */,
 				4B55CE4B1C3B3B0C0093A61B /* CSAtari2600.mm in Sources */,
 				4B55CE581C3B7D360093A61B /* Atari2600Document.swift in Sources */,
 				4B0EBFB81C487F2F00A11F35 /* AudioQueue.m in Sources */,
 				4BBB14311CD2CECE00BDB55C /* IntermediateShader.cpp in Sources */,
+				4B886FF51D03B61E004291C3 /* CSVic20.m in Sources */,
+				4B73C71A1D036BD90074D992 /* Vic20Document.swift in Sources */,
 				4BBF99181C8FBA6F0075DAFB /* TextureTarget.cpp in Sources */,
 				4BC76E691C98E31700E6EF73 /* FIRFilter.cpp in Sources */,
 				4B55CE5F1C3B7D960093A61B /* MachineDocument.swift in Sources */,
@@ -1736,6 +1764,14 @@
 			path = ..;
 			sourceTree = "<group>";
 		};
+		4B73C71B1D036C030074D992 /* Vic20Document.xib */ = {
+			isa = PBXVariantGroup;
+			children = (
+				4B73C71C1D036C030074D992 /* Base */,
+			);
+			name = Vic20Document.xib;
+			sourceTree = "<group>";
+		};
 		4BB73EA51B587A5100552FC2 /* Atari2600Document.xib */ = {
 			isa = PBXVariantGroup;
 			children = (
diff --git a/OSBindings/Mac/Clock Signal/Base.lproj/Atari2600Document.xib b/OSBindings/Mac/Clock Signal/Base.lproj/Atari2600Document.xib
index 9e73f7195..e1f140fda 100644
--- a/OSBindings/Mac/Clock Signal/Base.lproj/Atari2600Document.xib	
+++ b/OSBindings/Mac/Clock Signal/Base.lproj/Atari2600Document.xib	
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="9532" systemVersion="15E65" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
+<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="9532" systemVersion="15F34" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
     <dependencies>
         <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="9532"/>
     </dependencies>
diff --git a/OSBindings/Mac/Clock Signal/ClockSignal-Bridging-Header.h b/OSBindings/Mac/Clock Signal/ClockSignal-Bridging-Header.h
index 552a4cbd4..c87782a47 100644
--- a/OSBindings/Mac/Clock Signal/ClockSignal-Bridging-Header.h	
+++ b/OSBindings/Mac/Clock Signal/ClockSignal-Bridging-Header.h	
@@ -3,8 +3,10 @@
 //
 
 #import "CSMachine.h"
+
 #import "CSAtari2600.h"
 #import "CSElectron.h"
+#import "CSVic20.h"
 
 #import	"CSOpenGLView.h"
 #import "AudioQueue.h"
diff --git a/OSBindings/Mac/Clock Signal/Documents/Atari2600Document.swift b/OSBindings/Mac/Clock Signal/Documents/Atari2600Document.swift
index e13fff8fa..fd546a79b 100644
--- a/OSBindings/Mac/Clock Signal/Documents/Atari2600Document.swift	
+++ b/OSBindings/Mac/Clock Signal/Documents/Atari2600Document.swift	
@@ -26,17 +26,9 @@ class Atari2600Document: MachineDocument {
 	}
 
 	override var windowNibName: String? {
-		// Returns the nib file name of the document
-		// If you need to use a subclass of NSWindowController or if your document supports multiple NSWindowControllers, you should remove this property and override -makeWindowControllers instead.
 		return "Atari2600Document"
 	}
 
-	override func dataOfType(typeName: String) throws -> NSData {
-		// Insert code here to write your document to data of the specified type. If outError != nil, ensure that you create and set an appropriate error when returning nil.
-		// You can also choose to override fileWrapperOfType:error:, writeToURL:ofType:error:, or writeToURL:ofType:forSaveOperation:originalContentsURL:error: instead.
-		throw NSError(domain: NSOSStatusErrorDomain, code: unimpErr, userInfo: nil)
-	}
-
 	override func readFromData(data: NSData, ofType typeName: String) throws {
 		atari2600.setROM(data)
 	}
diff --git a/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift b/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift
index e752f032f..3f8e8ec60 100644
--- a/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift	
+++ b/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift	
@@ -114,4 +114,9 @@ class MachineDocument: NSDocument, CSOpenGLViewDelegate, CSOpenGLViewResponderDe
 	func keyDown(event: NSEvent) {}
 	func keyUp(event: NSEvent) {}
 	func flagsChanged(newModifiers: NSEvent) {}
+
+	// MARK: NSDocument overrides
+	override func dataOfType(typeName: String) throws -> NSData {
+		throw NSError(domain: NSOSStatusErrorDomain, code: unimpErr, userInfo: nil)
+	}
 }
diff --git a/OSBindings/Mac/Clock Signal/Documents/Vic20Document.swift b/OSBindings/Mac/Clock Signal/Documents/Vic20Document.swift
new file mode 100644
index 000000000..08b9b6bc0
--- /dev/null
+++ b/OSBindings/Mac/Clock Signal/Documents/Vic20Document.swift	
@@ -0,0 +1,24 @@
+//
+//  Vic20Document.swift
+//  Clock Signal
+//
+//  Created by Thomas Harte on 04/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+import Foundation
+
+class Vic20Document: MachineDocument {
+
+	private lazy var vic20 = CSVic20()
+	override func machine() -> CSMachine! {
+		return vic20
+	}
+
+	// MARK: NSDocument overrides
+	override init() {
+		super.init()
+		self.intendedCyclesPerSecond = 1022727
+		// TODO: or 1108405 for PAL; see http://www.antimon.org/dl/c64/code/stable.txt
+	}
+}
diff --git a/OSBindings/Mac/Clock Signal/Info.plist b/OSBindings/Mac/Clock Signal/Info.plist
index 07d3a41d5..3fbd5f02d 100644
--- a/OSBindings/Mac/Clock Signal/Info.plist	
+++ b/OSBindings/Mac/Clock Signal/Info.plist	
@@ -74,6 +74,20 @@
 			<key>NSDocumentClass</key>
 			<string>$(PRODUCT_MODULE_NAME).ElectronDocument</string>
 		</dict>
+		<dict>
+			<key>CFBundleTypeExtensions</key>
+			<array>
+				<string>prg</string>
+			</array>
+			<key>CFBundleTypeName</key>
+			<string>Vic-20 Cartridge</string>
+			<key>CFBundleTypeRole</key>
+			<string>Viewer</string>
+			<key>LSTypeIsPackage</key>
+			<integer>0</integer>
+			<key>NSDocumentClass</key>
+			<string>Vic20Document</string>
+		</dict>
 	</array>
 	<key>CFBundleExecutable</key>
 	<string>$(EXECUTABLE_NAME)</string>
diff --git a/OSBindings/Mac/Clock Signal/Wrappers/CSVic20.h b/OSBindings/Mac/Clock Signal/Wrappers/CSVic20.h
new file mode 100644
index 000000000..039e6afb0
--- /dev/null
+++ b/OSBindings/Mac/Clock Signal/Wrappers/CSVic20.h	
@@ -0,0 +1,13 @@
+//
+//  CSVic20.h
+//  Clock Signal
+//
+//  Created by Thomas Harte on 04/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#import "CSMachine.h"
+
+@interface CSVic20 : CSMachine
+
+@end
diff --git a/OSBindings/Mac/Clock Signal/Wrappers/CSVic20.m b/OSBindings/Mac/Clock Signal/Wrappers/CSVic20.m
new file mode 100644
index 000000000..64d7cdb49
--- /dev/null
+++ b/OSBindings/Mac/Clock Signal/Wrappers/CSVic20.m	
@@ -0,0 +1,13 @@
+//
+//  CSVic20.m
+//  Clock Signal
+//
+//  Created by Thomas Harte on 04/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#import "CSVic20.h"
+
+@implementation CSVic20
+
+@end