I have a 2019 iMac. It is a magnificent slab of aluminum and glass, housing a 5K Retina display that is so sharp it could probably perform eye surgery. It is a beautiful thing to look at—sleek, minimalist, and expensive. But there is a snag. The silicon brains inside are now so ancient they struggle to load a basic weather report without having a small digital heart attack.
Naturally, the “experts” on the internet—the sort of people who spend their weekends debating the merits of different types of thermal paste—have a solution. “Don’t throw it away!” they squeal. “Use it as an external monitor for your new Mac Mini or Macbook!”
It sounds like a brilliant, eco-friendly masterstroke. But in reality, it is a pursuit of total madness. Here is why every single option *that is currently available is, quite frankly, a non-starter.
In the olden days, Apple engineers were occasionally allowed to speak to humans. During that brief window of lucidity, they created Target Display Mode. You took a specialized cable, connected two machines, and—with a simple keystroke—the iMac became a monitor. It was fast, it was reliable, and it was clever.
But then, the world moved on to Retina. My 2019 iMac has a 5K display, which means it has 14.7 million pixels. To move that much data from a laptop to a screen in real-time, you need a pipe with the bandwidth of the Hoover Dam.
The technical reality is that the internal “Display Controller” inside these 2019 models is hard-wired specifically to talk to the iMac’s own brain. To make it talk to an external laptop instead, Apple would have had to install a massively expensive, high-bandwidth “multiplexer” chip that could switch between internal and external signals at 5K resolutions.
They looked at the cost, looked at the complexity of routing that much data without the screen catching fire, and simply said, “No.” Because of the sheer physics of pushing 5120 x 2880 pixels through a single port using 2019-era hardware, Target Display Mode wasn’t just “retired”—it was technically impossible. So, you are left with a 5K masterpiece that is fundamentally incapable of listening to anything other than its own aging, stuttering heart.
Then there is the software “fix.” With macOS Monterey, Apple introduced AirPlay to Mac. “Look!” they said, “You can beam your screen wirelessly!”
There are two massive problems here. First, to act as an AirPlay receiver, a Mac officially needs to be from 2019 or later. My 2019 model is two years too old. It’s like trying to get a vintage typewriter to send a WhatsApp message. Second, even if you use a “patcher” to force the feature onto old hardware, the results are catastrophic. Because it’s sending video data over a network, there is a delay. You move your mouse, and the cursor on the screen follows several minutes later. Trying to edit a document with that level of lag is like trying to play darts while wearing a blindfold and standing in a different zip code.
Next, we enter the world of hardware workarounds like Luna Display. This involves buying a small, $130+ plastic plug that you stick into your modern computer to trick it into thinking a monitor is attached. Then, you run an app on the old iMac to “stream” that footage.
Over one hundred dollars for a piece of plastic the size of a grape. And for that privilege, you still have to have the old iMac fully powered on, running its own entire operating system, fans spinning, sucking up electricity like a stadium floodlight, just to show a picture of a spreadsheet. It’s a wildly inefficient way to live your life. And to top it off, the image is laggy, and if you try and use this as your primary Mac Mini monitor, you get into this chicken and egg fight of which OS needs to start first so the ‘sending’ software talks to the ‘receiving’ software. It’s a nightmare that will see you throw it back in the box it came in and slap a ‘return to sender’ sticker on it. I know, because I’ve tried that as well.
Finally, there is the DIY crowd. They suggest you buy a “Controller Board” from a website in Melbourne that hasn’t been updated in three years or, more reliably, MacFixit. You are expected to use heavy-duty suction cups to rip the glass off the front of the iMac, tear out the motherboard, the speakers, and the power supply, and then manually wire the screen to this new board.
This requires the steady hands of a neurosurgeon and the electrical knowledge of Nikola Tesla. One slip of the screwdriver and you’ve turned a beautiful, albeit slow, computer into a very large, very sharp pile of electronic waste. And once you’re done, you have a nest of exposed wires and a separate power brick dangling off the back. It looks like something built by a madman in a cave and the cost, after all of that, would have bought you a real monitor from Officeworks.
Attempting to “repurpose” an iMac as a monitor is a noble goal, but it’s like trying to turn a vintage grand piano into a coffee table. Yes, you can do it, but the effort, the cost, and the sheer technical faff mean you’d be much better off just buying a proper table in the first place.
If you have an old iMac, put it in the guest bedroom and let it pretend to be useful. But don’t try to make it a monitor. It’s over. Let it go.
