How do you add a second display to one of Apple’s new Thunderbolt iMacs?

With a monitor size of either 21.5 or 27 inches the new Apple iMacs offer a lot of screen space (1,920-by-1080 resolution on the 21.5-inch iMac, and a whopping 2,560-by-1,440 on the 27-inch iMac), but many Mac users need even more and use a second or even third display to maximize their screen volume.

Adding a second display used to be pretty easy – just find the Mini DisplayPort at the back of the iMac, and plug in a Mini DisplayPort to DVI or VGA adaptor to connect the second display.

Every Mac with a Mini DisplayPort allows you to connect an external display or projector using an adaptor. You can use an external display as your main workspace or to extend your desktop, or you can work in mirrored mode with a projector so you can view what your audience sees.

But look at the back of one of Apple’s latest iMacs and you won’t find anything that looks like a display port.

Instead you get a row of four USB 2.0, one FireWire 800, and two fancy new Thunderbolt connectors, plus a Gigabit Ethernet slot, and Audio In and Out ports. No DisplayPort, mini or maxi.

How can you attach a second display or a projector to a new iMac, MacBook Pro or MacBook Air? Or a Mac mini for that matter?

Apple Thunderbolt iMac ports

Where’s the DisplayPort?

Apple’s very proud of the fact that Thunderbolt is more than just a new high-speed data connector but it doesn’t make very clear that it is also a video standard.
Thunderbolt is based on high-resolution DisplayPort technology so any Mini DisplayPort display plugs right into the Thunderbolt port. To connect a DisplayPort, DVI, HDMI, or VGA display, just use an existing adaptor.

Most modern displays use DVI so you’ll need Apple’s Mini DisplayPort to DVI Adapter, or Mini DisplayPort to VGA Adapter for older analogue monitors or projectors.
Apple says these adaptors are compatible only with Mac computers with Mini DisplayPort. But it doesn’t make clear that they are also compatible with Macs and MacBooks with a Thunderbolt connection as it’s the same thing. Apple could have made this much easier to understand if it had added a Mini Display Port icon above the Thunderbolt icons on the backs of the new Macs or sides of MacBook Pro.

Because the new 27-inch iMac has two Thunderbolt ports you can attach two external displays for all-round screen vision.