An old iMac makes a fine monitor for a MacBook or a Mac mini, except that it starts like a computer: it stops at the login screen and waits for a password, then for someone to open an app. That means a keyboard and mouse on the desk just to turn the screen on. Second Display can make the iMac skip all of that and start straight as a display, like a monitor.

What “start as a display” gives you

  • Switch it on, and it’s a display. No login screen, no password, no app to open. The iMac comes up ready for your Mac.
  • No keyboard or mouse on the desk. The iMac needs none of its own to start as a display.
  • Your Mac connects as always, over a Thunderbolt cable or your network, and the picture appears.
  • Nothing of yours changes. Your own files, apps and settings on the iMac stay as they are.
  • It’s your choice, any time. Turn it on when you first set up Second Display or later in Settings, and turn it off whenever you like.

Before you start

  • Two Macs that work with Second Display. The iMac needs macOS 12.3 or later, the Mac you work on macOS 14 or later. What you need
  • Second Display in the Applications folder on the iMac. If it runs from the disk image or from Downloads, the setup says so.
  • FileVault needs to be off on the iMac. Second Display tells you if it isn’t.
  • An administrator’s name and password, which macOS asks for once.

Set it up, step by step

  1. Open Second Display on the iMac and choose Use this Mac as a display.

  2. At How should this Mac work as a display?, choose As soon as the Mac turns on. Already using Second Display? Open Settings › General on the iMac and click Set Up… next to Start as a display when this Mac turns on.

  3. Second Display checks the iMac. If something needs your attention first, it shows it with a button that takes you to the fix.

  4. Click Set Up and Restart…. Save your work first: the iMac restarts, and apps that are open quit without saving.

  5. macOS asks for an administrator’s name and password. Second Display shows each part of the setup with a check mark as it’s done.

  6. The iMac restarts and comes back as a display, waiting for your Mac. On macOS 15 and later macOS asks once whether Second Display may find devices on your network: click Allow. Allow Local Network access

From then on, turn the iMac on and connect from the Mac you work on. If that Mac isn’t set up yet, follow Set up Second Display on both Macs.

Every day

Switch the iMac on and it’s a display. While it waits, its screen sleeps like a monitor’s and lights up when your Mac connects. Sleep, wake and the lock screen

Over a Thunderbolt cable, the picture is lossless at Highest quality. Without one, Wi‑Fi, Ethernet and a USB‑C cable work too, with a compressed picture. Use Wi‑Fi or Ethernet

Turn it off

On the iMac, open Second Display Settings › General and click Stop Using…. Second Display guides you through it, and the iMac starts as usual again. Your files and apps stay as they are. You can turn it on again later with Set Up….

Compared with Target Display Mode

Target Display Mode never started by itself: the iMac had to be on, and someone pressed Command‑F2 on its keyboard. It also works only on iMacs from 2009 to mid 2014 with macOS High Sierra or earlier, and with a Mac from 2019 or earlier. Second Display works on iMacs from late 2015 on, with Intel or Apple silicon, and the iMac is a display from the moment it turns on. An alternative to Target Display Mode

Not sure your iMac qualifies? See which old iMacs can be a monitor. Starting as a display is part of Second Display, free for 7 days, then $39 once. Download it and try it on your iMac.

Questions

Do I need a keyboard and mouse on the iMac?

Not to start it. Turn the iMac on and it comes up as a display by itself. Keep a keyboard or mouse at hand for the setup, and on macOS 15 and later for one question after the first restart.

Which iMacs can start as a display?

Any iMac that runs macOS 12.3 or later, from the late 2015 models to iMac with Apple silicon. Other Macs with macOS 12.3 or later can too. The Mac you work on needs macOS 14 or later.

Do my own files and apps stay on the iMac?

Yes. Your files, apps and settings stay as they are, and you can still use the iMac as a computer whenever you want.

How do I turn it off?

On the iMac, open Second Display Settings › General and click Stop Using. Second Display guides you through it, and the iMac then starts as usual again.

Does it work over Wi‑Fi too, or only with a cable?

Both. Over a Thunderbolt cable the picture is lossless at Highest quality. Over Wi‑Fi, Ethernet or a USB‑C cable without Thunderbolt it works too, compressed to suit the connection.

Can I use several iMacs as displays?

Yes. One Mac can drive several displays at once, and each iMac you use as a display can start as one.

Does it cost extra?

No. It’s part of Second Display: free for 7 days, then $39 once, with every future update included.