iMac 2011 21.5-inch as a second screen for a MacBook.
What works, and what to buy.
Yes, a 21.5-inch iMac from 2011 can be a second screen for a MacBook with M1, M2, M3 or M4. It needs an app such as Encore, because Target Display Mode doesn't accept a Mac from 2020 or later. For a sharp picture, connect the two with Thunderbolt or Gigabit Ethernet. Wi-Fi works too, at lower quality.
Which 2011 iMac do you have?
Apple made two 21.5-inch iMacs in 2011: the Mid 2011 and the Late 2011. On the iMac, open the Apple menu and choose About This Mac. You'll see a line such as "iMac (21.5-inch, Mid 2011)".
Both models share what matters here. They run up to macOS 10.13 High Sierra. They have a Thunderbolt port and Gigabit Ethernet. They were the first iMacs with Thunderbolt, which gives you more cable options than older models. Everything below applies to both, and the 2011 iMac page has the full details.
Can a 2011 iMac be a monitor for an M1 MacBook?
Yes, but not the way many people remember. Pressing Command-F2 starts Target Display Mode, and every 2011 iMac supports it over Thunderbolt. The catch is the other Mac.
Apple's rule is that the connecting Mac must be introduced in 2019 or earlier and run macOS Catalina 10.15.8 or earlier. Every MacBook with Apple silicon falls outside that rule. In a 2020 MacRumors thread, someone tried an M1 Mac mini with a 2011 iMac over Apple's adapter. They wrote "Nothing Happened".
If your MacBook is an Intel model from 2019 or earlier, still on Catalina, Target Display Mode is the better choice. It is free and shows the signal directly. Encore vs Target Display Mode lists Apple's exact rules. For any newer MacBook, you need software that sends the picture over the network or a cable.
How to use a 2011 iMac as a second screen with Encore
- Check the iMac's macOS.Encore Receiver needs macOS 10.13 High Sierra or later. That is the newest macOS a 2011 iMac runs, so update to it first if the iMac is on something older.
- Install both apps.Encore goes on your MacBook, which needs macOS 14 Sonoma or later. Encore Receiver goes on the iMac. Both are on the download page.
- Get past the old browser.The iMac's old Safari can't show every page. The install guide has a light page for it, and the one-time macOS warning.
- Connect a cable if you can.The table below shows what to buy. Wi-Fi works without one.
- Pair once.The iMac shows a 4-digit code. Type it on your MacBook. After that, the two connect by themselves.
- Arrange the screens.The iMac shows up as an extra display in System Settings, Displays. Drag windows onto it like any monitor.
Which cable connects a MacBook to a 2011 iMac?
Every recent MacBook has USB-C ports. The 2011 iMac has neither USB-C nor HDMI input, so you need one of two routes. The link must carry at least 400 Mbps end to end.
| Route | What to buy | What you get |
|---|---|---|
| Thunderbolt | Apple's Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter, and a Thunderbolt cable to the iMac's Thunderbolt port | Several Gbit/s: the sharp, lossless picture |
| Gigabit Ethernet | A USB-C to Gigabit Ethernet adapter that says Gigabit or 10/100/1000, and a Cat6 cable (Cat5e also works) | Up to 1000 Mbit/s: the sharp, lossless picture |
| Wi-Fi | Nothing | Works, at lower quality |
The slowest part counts: adapter, hub, cable and router port.
Three traps catch people. A USB-C charging cable carries no picture. A cheap 10/100 Ethernet adapter stays below 400 Mbps. And an adapter in a hub can keep dropping the link, so plug it straight into the MacBook. The cable guide covers every case.
Wi-Fi or cable on a 2011 iMac
Wi-Fi is the easy start, but this iMac is a hard case for it. iMacs from 2009 to 2012 use 802.11n Wi-Fi. Realistic 5 GHz Wi-Fi gives about 50 to 400 Mbps, and 2.4 GHz never gives a sharp picture.
- Over Wi-Fi: it works with nothing to buy. The picture is always lower quality than on a cable, and it is compressed while things move. Keep both Macs on 5 GHz, near the router.
- Over a cable: the sharp, lossless picture. The iMac's keyboard and mouse can control your MacBook, which they can't over Wi-Fi.
- Sound plays on the iMac's speakers over both.
If you plan to use the iMac as a monitor every day, buy the cable. Wi-Fi or cable for a second screen explains the difference in detail.
What you get on the 21.5-inch 2011 iMac
- An extra desktop up to the panel's size at 60 fps. That is what we expect on this model, not yet measured on every unit.
- Its keyboard and mouse for your MacBook, over a cable. Press Control-Option-Command-Esc on the iMac to switch back.
- Its speakers for your MacBook's sound.
- StandBy when you stop: a clock, the weather and your calendar, or AirPlay music with the album cover.
What a 2011 iMac can't do
An old iMac is not a new monitor, and some limits are worth knowing before you buy anything.
- No Retina panel. Retina iMacs start in 2014. Text on this panel looks coarser than on your MacBook's Retina screen.
- Ultra may not appear. Ultra sends every frame as ProRes 4444 over a cable. Encore measures whether the iMac can decode it in time, and only offers it when it can.
- No camera or microphone yet. Using the iMac's camera and microphone from your Mac is coming soon, over a cable only.
- No latency figures yet. Encore has not published latency measurements. We will publish them per iMac model.
- Power. An old iMac draws far more than a modern monitor. Apple's idle power figures list 135 to 142 W for the 27-inch Mid 2011. Check your own model on that page.
Other ways to use this iMac
Encore isn't the only app. Luna Display supports iMacs from 2011 on, with a dongle: see Encore vs Luna Display. Every way to use an old iMac as a monitor compares the rest, with sources.
Something not connecting? The troubleshooting page has the fix for each message Encore shows.
Questions
Can a 21.5-inch 2011 iMac be a monitor for an M1 MacBook Air?
Yes, with an app such as Encore, over Wi-Fi or a cable. Target Display Mode won't work, because Apple requires the connecting Mac to be from 2019 or earlier on macOS Catalina or older.
Does the 21.5-inch 2011 iMac have Target Display Mode?
Yes. Every 2011 iMac supports it over a Thunderbolt cable, while the iMac runs High Sierra 10.13.6 or earlier. The other Mac must be from 2019 or earlier on Catalina 10.15.8 or earlier.
Which cable connects a USB-C MacBook to a 2011 iMac?
Apple's Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter and a Thunderbolt cable, or a USB-C to Gigabit Ethernet adapter and a Cat6 cable. A USB-C charging cable won't work. Full guide.
Is Wi-Fi good enough for a 2011 iMac as a second screen?
It works with nothing to buy, but the picture is always lower quality than over a cable. The 2011 iMac has 802.11n Wi-Fi, and its keyboard and mouse only work for your MacBook over a cable.
What does Encore cost?
Encore is free during the public beta.