Clock Signal


Clock Signal is an open source 68000 Apple Macintosh emulator. Using Clock Signal (along with the appropriate ROM image) it is possible to emulate a Mac 512ke or Plus. Builds are available for macOS and it will compile from source for other UNIX-esque platforms.

In addition to the Macintosh it emulates a bunch of other platforms, including the Apple II.

Getting Started

Download the Latest Version

Binary Releases

The latest macOS binaries are always available from here.

Building from Source

Clock Signal's development repository is hosted on GitHub; the latest code can always be pulled from master.

Because it is a native Cocoa application, no further dependencies are required to build for macOS — just open the Xcode project in `OSBindings/Mac` and use the ordinary Xcode build procedure.

For kiosk mode dependencies are:

  • SDL;
  • zlib; and
  • SConstruct, to build.

Simply `cd` into `OSBindings/SDL` and run `scons`.

Initial Launch


Although it opts in for sandboxing, the application is not signed. So if you have GateKeeper set to its default settings, locate the icon, right click on it and select 'Open…'. On the GateKeeper prompt that appears, select 'Open'.

By default the emulator will show an open file dialogue. From there the easiest way to get a running Macintosh is to locate a bootable floppy disk (400kb or 800kb) or hard disk image and select it.

A window will appear with a sheet prompting you that the emulator requires you to provide images of the system ROMs and asking you to drag and drop a copy onto that dialogue. Locate a copy of the Macintosh Plus ROM and drag and drop it — the file name doesn't matter. The emulator will take a copy of the ROM you supply, so you need do this only once, and will continue booting the machine.


SDL builds do not provide a UI; the intention is that the user set up file associations in their preferred file browser, or else start the emulator with `clksignal image.dsk`. By default it will search for the system ROM in `/usr/local/share/CLK/` and `/usr/share/CLK/`; if neither of those is convenient then you may specify any other location you prefer via the `–rompath` command-line argument. It will check those paths for a file named `Macintosh/macplus.rom`.

Inserting Alternative Disks

Drag and drop a disk image onto the emulator's window to boot it. On the macOS version you can also use the keyboard shortcut command+shift+I. The emulated Mac has only two floppy drives, so you may need to eject something first.

This procedure works at any time: if the disk you supplied at launch is not bootable, the emulated Macintosh will show the flashing question mark prompt. Locate a bootable floppy disk and drag and drop it onto the emulator's window to continue.

Using Hard Disks

This works exactly like a real Mac: the hard disk must have a System folder on it to be usable. If it does not, boot with a floppy disk and copy the System folder over. If the hard disk is not yet formatted for Mac use, boot a disk with the Apple HD SC Setup application on it and format the hard disk first.

Just like on a real Macintosh, a hard disk must be present from power-up and cannot be ejected.

Intended Usage After Initial Setup

Having configured a suitable hard disk, double click it to launch the emulator and boot from that hard disk.


clocksignal.txt · Last modified: 2019/09/23 18:19 by tomharte
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