Some computing challenges are easy. Connecting external displays to a Mac, unfortunately, isn't always one of them.
To be fair, Apple tries to make it easy. Once you successfully determine the physical connection required, OS X Yosemite rather elegantly adjusts for the second display. But the trick is navigating the required physical connections.
The options available for connecting external displays to your Mac depend, understandably, on the Mac model you own. Age plays a factor, too. For example, new MacBook Pros boast two Thunderbolt ports and HDMI connectivity, whereas MacBook Pros only a few years old possess a single Thunderbolt port and no HDMI connectivity.
Apple users seeking to deploy a second monitor using a Mac must determine the specific Mac model they are using and catalog the available ports. While third-party electronic boxes are available that technically make it possible to connect external displays using their own proprietary technology, refresh rate, resolution and color matching issues sometimes make such solutions unreliable and problematic.
So, I recommend avoiding the third-party external video box option. Next, determine which displays are compatible with your Mac's ports, because trying to connect a MacBook Pro's HDMI port to a VGA-,DVI- or VGA- and DVI-only compatible display will prove to be an exercise in frustration. However, you can use Apple's Mini DisplayPort to DVI adapter, for only $29.00 (USD), to connect a Dell (or other manufacturer's) DVI-compatible display to your Mac's Thunderbolt port (Apple also offers a $29.00 Mini DisplayPort to VGA adapter).
See? I told you it got complicated.
Adding a single external display
Adding one external monitor to most Macs less than two or three years old is fairly straightforward. The connection is particularly easy if you're using an Apple Thunderbolt display. At $999.00, the 27" displays are pricey. All you need to do, though, is connect the display to your Mac's Thunderbolt port, and you should find yourself good to go.
When all you have is a VGA- or DVI-compatible display, which is a fairly common occurrence, you should leverage Apple's Mini DisplayPort adapter mentioned earlier. The Mini DisplayPort can be plugged in to the Mac's Thunderbolt port to enable physically connecting the second display.
In situations where your Mac possesses an HDMI port, you can leverage the HDMI standard to connect a second display. Worth noting, too, is the fact Apple sells Belkin's 4K Mini DisplayPort to HDMI adapter. The $34.95 adapter is advertised as being able to connect a MacBook to an HDTV for sending both digital audio and 4K video to the HDMI display from 2010 and newer Macs (older models require a separate cable for digital audio).
Connecting multiple displays is where the process becomes even more complex. The specific model Mac makes a significant difference as to the compatibility supported. I recommend any user unsure of setup, including graphic card, put their AppleCare warranty to use and contact Apple at 800-275-2273.
New MacBook Pro Retina models, both 13" and 15" versions, support using the built-in display and two external displays. The built-in display can support full native resolution, while the laptops can power resolution up to 2560 by 1600 on the external monitors. New MacBook Airs, however, only support full native resolution on the built-in display and one external monitor.
Keeping track of external display options for desktop Macs, including Apple's flagship Mac Pro, almost requires a scorecard. As of this writing, the iMac supports the use of the built-in display and one external monitor up to 30". The Mac mini supports up to two displays. The Mac Pro, meanwhile, supports up to three 4K displays or six Thunderbolt displays.
Most manufacturers' displays should prove compatible. If you can justify Thunderbolt monitors, however, they simplify the process and deliver first-rate graphics. Plus, Thunderbolt displays are more than just monitors; they also serve as a de facto docking station capable of also powering Mac laptops via its Thunderbolt- and MagSafe-equipped twin plug, among other features. Apple maintains a handy chart on its website listing which Macs support how many Thunderbolt displays, should you wish to further research.
Erik Eckel owns and operates two technology companies. As a managing partner with Louisville Geek, he works daily as an IT consultant to assist small businesses in overcoming technology challenges and maximizing IT investments. He is also president of Eckel Media Corp., a communications company specializing in public relations and technical authoring projects.