RetinaRelay — A second life for your iMac

Wired setup

Whatever you plug in, it measures it.

There are three good ways to connect two Macs, and they are not equally fast. RetinaRelay measures the one you gave it, opens on the best picture that connection can hold, and adjusts if the picture starts costing more than the cable has — so you get your hardware's best without tuning anything.

Recommended cables

Thunderbolt — the best there is

About 15 Gbps between two Macs, more than ten times what a 5K picture at 60 fps needs. macOS brings up Thunderbolt Bridge on its own. Nothing gets compromised.

USB SuperSpeed — the best value

A plain USB 3 cable carries full 5K at 60 fps, with no adapter and nothing to configure. Every Mac we support has a USB 3 port, so this route always works.

Gigabit Ethernet — and you may own it

Every 2012–2015 iMac has an Ethernet port, and a direct cable needs no router or switch. Native 5K at 60 fps, with some fine detail traded away on heavy video.

Low latency

Your screen reaches the iMac fast enough that dragging a window feels like dragging it on a monitor, not like operating one over a wire. The Host shows you the figure it is actually achieving, next to what a real external monitor manages.

No codec, no compression artefacts

Instead of encoding video, RetinaRelay compresses each frame into a GPU texture format your iMac's graphics hardware unpacks for free. Nothing queues up in an encoder, so nothing has to catch up.

Native macOS

Built on ScreenCaptureKit and Metal, with real macOS interfaces in both apps. No Electron, no bundled runtime, and one permission to grant — Screen Recording, and nothing else.

1

Install Host on your Mac

Drag the Host app to Applications. Grant Screen Recording permission on first launch. The menu bar icon appears, and you're set.

2

Install Viewer on your iMac

Drag the Viewer app to Applications on your older iMac. Open it. It waits for the Host. No IP entry, no setup wizard.

3

Connect a cable. Click Start.

Thunderbolt, USB SuperSpeed, or a gigabit Ethernet adapter between the two Macs. The Host is found automatically — no IP addresses. Pick Extended or Mirror, hit Start, and RetinaRelay works out the quality itself.

The Viewer app

Invisible when it's working.

The Viewer keeps a small status window while it waits, then disappears into fullscreen the moment the stream is live. No persistent overlay, nothing sitting on top of your desktop.

And when the picture does stop, it says why in plain English — your Mac went to sleep, streaming was stopped, RetinaRelay was quit — with the one thing to do about it. No spinner, no guessing.

RetinaRelay Viewer

The pointer

The cursor doesn't lag. It can't.

Your pointer is never part of the picture. RetinaRelay moves the iMac's own cursor instead, so macOS draws it on the same hardware layer it uses for a real display — at the panel's full refresh rate, independent of everything else.

Which is why the pointer stays glassy even in the rare moment the picture is working hard. If you want the numbers, there's a live overlay for that too.

Connected 5120×2880 60 fps Thunderbolt BC7 mode 6

Sound comes with it

Turn on one switch and your Mac's audio plays through the iMac's speakers — volume keys, mute, and the macOS volume UI all drive it natively, because RetinaRelay installs a real audio device rather than eavesdropping on one.

Close the lid

With the iMac connected and your Mac on power, shut the laptop and keep working — the iMac becomes your only display and nothing goes to sleep. No password on the way back, because nothing ever slept.

Sleep and wake, properly

Let your Mac sleep and the iMac says so, in words, instead of freezing on the last frame. Wake it and the picture comes back on its own — no reconnecting, no restarting either app.

Host Mac

Viewer (iMac / older Mac)

macOS

13 Ventura or newer

10.15 Catalina or newer

Hardware

M-series or Intel Mac

iMac Late 2012 or newer

Quality

Measured from the cable, automatically

Up to native 5K at 60 fps

Connection

Thunderbolt, USB SuperSpeed, or gigabit Ethernet

Thunderbolt, USB SuperSpeed, or gigabit Ethernet