How to Run Apple I on Your Mac Using OpenEmulator

The Apple I was Apple's first computer, and you can experience computing history by emulating it with OpenEmulator. Here's how.

Apple I is the first Apple computer, created by Steve Wozniak and Steve Jobs in 1976 in Jobs' parents' garage. The Apple I was based on a low-cost MOS Technology processor called the 6502, running at 1 MHz.

Many personal computers and game consoles of the 1970s and 1980s were based on the 6502. In fact, since it was the first low-cost processor of the time, the 6502 was what enabled the personal computing revolution. happen at all.

The Apple I was rudimentary – one large motherboard sold as a kit, without a power supply, keyboard or display – these parts were left up to the user to assemble or supply.

The Apple I had limited graphics capabilities and no sound. At that time, CRT monitors were mostly closed-circuit CRT monitors with green or amber text displays.

For I/O, the Apple I had one separate connector on the side, designed to work with the cassette port. Programs could be saved and loaded back into the machine from tape. At that time, disk drives were not used except on large mainframe computers.

The Apple I had virtually no built-in OS or software—when the computer was turned on, the monitor prompt appeared in assembly language, and the user had to know how to use 6502 assembly language. A BASIC programming interpreter could also be downloaded if necessary.


Several modern Apple I printed circuit board (PCB) clones have appeared recently, including the one we reviewed in the previous article article.

Today you can build your own working copy of the Apple I on a printed circuit board, using modern parts and ROM flashed from the original sources.

But creating an Apple I clone requires at least basic knowledge of electronics, component soldering techniques and a little about serial communication – something that not everyone can have.


If you're not ready to create your own Apple I clone, there is a much easier and faster way to run the Apple I software : emulation.

Emulator apps allow you to run older operating systems and software on modern hardware, including a Mac. There are many emulators available, but for Apple I software, the best one by far is OpenEmulator from the OpenEmulator Project.

Originally written by Mark Ressl in 2009, OpenEmulator also allows you to emulate Apple I's successors – the Apple II and Apple II Plus – and a third model, the Apple III, which was one of Apple's biggest failures.

The download link on the OpenEmulator website connects you to an Internet Archive page where you can download the latest version of OpenEmulator and its source code.

Using OpenEmulator

OpenEmulator comes with three built-in Apple I emulators:

  1. Original Apple I 'Woz'
  2. Modern copy of Achatz A-ONE Apple I
  3. Replica Briel-1

The second and third models are modern third-party versions of Apple I hardware that you can purchase online.

In this article we will use the original Voz model. Launch OpenEmulator and select its icon in the picker, then click Select.

OpenEmulator in action.

This boots the Apple I in a window and leaves you at the Monitor Command Prompt (also known in its day as Wozmon). . You'll need to know 6502 assembly language and be able to use hexadecimal numbers to enter code or load programs from a file, which we'll get to shortly.

Apple I Documentation

Apple originally provided a User's Guide, a Cassette Guide, and a Programming Guide in BASIC for the Apple I. Many of these documents can still be found on the Internet.

It's a good idea to look at the user manual to see how the Apple I works.

One such good source of documentation is the DigiBarn Computer Museum. DigiBarn has a ton of useful information about the Apple I, including links to other sites, photos, and additional information. DigiBarn also has fully restored versions of the original documentation, including the original cassette manual.

Another incredibly cool Apple I site is the Apple-1 Registry, which has all sorts of background information on the Apple I. This includes prototype information, an amazing collection of original Apple I photos, and an insanely great Apple I Museum section , which features the original Apple I computers found in museums around the world today.

One such museum is the Computer History Museum in Mountain View, California, north of Cupertino. The Apple Park campus in Cupertino also has the original Apple I. has a large gallery of original Apple cassette labels.

Loading cassette programs

The original Apple I had an additional cassette circuit board that connected to motherboard edge connector on the right side. Cassettes, officially known at the time as compact cassettes, were a new analog audio cassette format for music in the 1970s.

Portable cassette recorders soon appeared, as well as cassette players for home audio systems and cars. Sony's world-famous Walkman music player was based on the compact cassette.

Cassettes worked by electrically encoding sound onto a magnetic tape and passing the tape through an electromagnetic record/playback head inside cassette players. The tape was driven by a small motorized rubber wheel and a metal spindle that clamped and pulled the tape into the cassette during playback/recording.

Cassettes could be rewound or rewinded using the controls of cassette players.

Computer manufacturers of the 1970s soon realized that they could encode computer program data through sound and store it on cassette tapes just like music. During playback, the computer could listen to the cassette player's headphone port and decode programs from the recorded audio.

If you play a tape of a computer program on a cassette player and listen to it, you will hear an electronic screeching sound that represents data in electromagnetic form.

All this was before data was stored directly in digital format.

Early Apple program on cassette.

The Apple I cassette circuit board had analog audio ports for both recording and playback for connection to standard cassette players via an audio cable. .

Most personal computers of the 1980s worked this way, and the cassette drive soon became the standard format for computers of that era. All this was before disk storage became widespread.

Apple I cassette circuit board.

Apple itself sold several Apple I programs on cassettes that users could buy and load onto their Apple I computers. Most Apple I cassette programs on tape contained initial information about the program in the header, followed by the actual program code, which the user could execute by entering the hexadecimal address into Wozmon on the Apple I.

Wozmon works in OpenEmulator.

The starting address of program code in Apple I binaries is known as the source address. Entering the source address followed by the letter “R” (for “Run”) into Wozmon after loading the program from tape or disk, and then pressingReturnruns the program.

Want to play a game?

Default , in OpenEmulator the cassette player is already connected and active.

To load a program from a binary or text file on disk, as if it were loaded from a tape, all you have to do is select File->Open in the line menu. select any suitable Apple I program file and run it.

As an example, we'll run an Apple I clone of the Wordle game called Worple, written by Jeff Jetton.

To get Worple, first go to its GitHub page, then use git to clone the repository, or download the zip file and extract it to your Mac's drive.

Open the resulting folder “apple1-worple” and open the file worple.txtin TextEdit. Don't change anything in the text. This file contains the 6502 assembly code that runs on the Apple I.

Note the first two bytes in the file: “0300”, this is the source address in hexadecimal. Going to this address in Wozmon launches the program.

Also note that at the very end of the file there is the text “0300R”. When OpenEmulator loads a file, it executes all the run commands automatically found at the end – in this case the instruction to run the code at hex number 0300.

Worple for Apple, I run in OpenEmulator .

Although Worple is only 11 KB in size, if you load it into the original Apple I emulator in OpenEmulator, it will take a while to load. Instead, use the Achatz A-ONE emulator by selecting File->New.from the OpenEmulator menu bar and then selecting that emulator in the template picker.

After downloading Achatz A-ONE, select File->Open from the menu bar, then select file worple.txtin the open file. panel. Achatz A-ONE will download and run the file just as if it were running on a real Apple I. Very cool.

OpenEmulator Hardware Library

In OpenEmulator, if you select Window-> “Show Devices”then View->Show Equipment Library in the menu bar, you will get two additional windows.

Show Devices displays a new window that shows all devices currently running or connected, including the current emulator, all peripherals, and expansion cards.

In the Peripherals section, the window shows which display is currently in use. Using the display slider, you can even change display characteristics such as brightness, contrast, etc.

The Hardware Library window shows all the possible built-in devices you can use with the emulator open, not just displays. . The Hardware Library window also displays other peripherals such as disk drives, printers, input controllers, and other expansion cards.

What's not immediately obvious is that to use one of the other peripherals, simply click and drag it out of the Hardware Library window and drop it into a new location in the Devices window:

Drag a device.

For displays, you can only use one display at a time, and if you drag a new one into the Devices window, the existing one will be replaced, although its contents will remain the same.

If you use a monochrome Studio monitor as your display, you'll even get distortion and scan lines from a retro-style glass tube display!

Exactly the same as in 1976.

Save the configuration

Finally, when your OpenEmulator is configured the way you want, you can save the entire configuration to a file with the extension “.emulation”. To do this, select File->Save from the File menu, then select a location on your disk, give the file a name, and click Save.

If you later want to reset your emulator settings, double-click the .emulation file in Finder and everything will return to its previous state.

Some additional resources

There is a lot of information about the Apple I Internet and many sites with a huge amount of information about the computer.

If you want to learn more about writing programs in 6502 assembler, pick up a good book on the subject, then visit the dasm 6502 assembler website. dasm started in the 1980s and is still popular today.

The Apple II history site has an Apple I page that contains a lot of information about the development, how the machine was sold, the hardware, and other notes.

The Apple II Documentation Project site has a large archive of Apple I documentation, including information on the A-One and Replica 1 computers, as well as the original Apple I.

A cool personal Apple blog I, dating from 2009, is located at and contains a lot of information.

Some additional information about the Apple I Cassette Interface Card for Replica I can be found on Hans Otten's website in the Netherlands.

Finally, to quickly run Apple I software over the Internet without having to launch a special application, use Will Scullin's Apple I JavaScript Emulator. It even includes several built-in Apple I programs.

OpenEmulator is a masterpiece, one of the best emulators available for Apple I, II and III computers. It lets you enjoy these iconic retro machines on a modern Mac for years to come.

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