It’s not unusual for people to travel with two computers: a laptop for work and a tablet for personal use. If this is you, and you wish for additional screen real estate when you’re using the laptop, there are applications that enable you to use an iPad as a second monitor for Windows and OS X computers.
Have Realistic Expectations
Before we begin, it’s important to understand that a tablet acting as a second monitor isn’t going to have the instant performance of an actual monitor hooked to a video-out port. An application running on the laptop is going to need to process the information being sent to the external screen and then communicate with a second app running on the iPad that will then show the content. This means there is going to be some delay between what the laptop sends and what shows up on the tablet.
The developers of the software described below have had some success minimizing this lag, but it’s an inevitable part of the process. If you need perfect performance, the only option is getting a real second monitor for your PC or Mac.
Also, keep in mind that running the second tablet is a strain for the notebook, especially if there’s a wired connection between it and the tablet, as the Windows or Mac computer will also be powering the iPad. This will dramatically reduce the time the notebook can go without being recharged, so it might be better to mostly use the dual monitor setup with the laptop plugged in.
This is an application when a Bluetooth keyboard might come in handy. Using a keyboard that’s physically attached to the laptop is doable, but it’s not an ideal way to make use of an external monitor. This is especially true when the external iPad’s screen is larger and higher resolution that the laptop’s, in which case it will make sense to use the iPad’s screen as the main one, and have the laptop’s display be the secondary display, even though the keyboard in this situation will be facing the secondary rather than the primary display. A Bluetooth keyboard communicating with the Windows or Mac computer won’t have this problem, but it will be another item to carry around.
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One option for turning an iPad into an external monitor for your laptop that has drawn a great deal of attention recently is Duet Display. It can run on any tablet or phone running iOS 7.0 or later, though it’s much more useful on a large tablet like an iPad Pro.
This software makes no attempt to be wireless; the laptop and the tablet (or phone) must be physically connected with a Lightning or 30-pin cable. The only setup required is going to All Settings > System > Display to arrange the monitors.
Our tests with a Microsoft Surface Pro 2 running Windows 10 were reasonably successful. There is a lag, but it’s short… about a quarter of a second. This is a bit distracting when watching video and the picture and audio aren’t quite synced, but has no effect on productivity applications. Writing in Microsoft Word or consulting an Excel spreadsheet works quite well on the iPad Pro’s larger display, freeing up the Surface’s screen for displaying email or other apps.
Installing and setting up Duet Display on the MacBook Pro was a straightforward process, and there almost no configuring to be done, aside from going to System Preferences > Displays > Arrangement and putting the external screen where it lines up nicely with the laptop. When our iPad Pro was connected, it took on a 1366 x 1024 pixel resolution, and we were not given the option to change that.
Unfortunately, the same lag that’s present in the Windows version also crops up in the OS X version. This is short — perhaps a quarter of a second — but noticeable, which is distracting when playing video. That said, the delay is short enough that it has no effect on productivity applications.
We had a commercial artist test working in Photoshop on an iPad Pro with Duet Display, and the lag meant that lines drawn with an Apple Pencil always appeared a bit behind where the pen was touching the screen. As a result, she found this very hard to work with, and would be a solution she’d only use in a pinch.
This application supports only wired connections, so for our Windows test the Surface tablet was connected to the iPad with a Lightning cable, but later tests with another app will show this is probably for the best.
When used with the iPad Pro, the Wired XDisplay offers a range of screen resolutions: 2048 x 1536 (native), 1536 x 1152, 1360 x 1024, and 1024 x 768. The external display can become the main display, and the screen can auto-rotate between portrait and landscape orientations. Splashtop’s app can also offers Low, Medium, and High framerates, as well as Normal and High Quality. These latter settings can reduce the demand on the Windows computer’s processor when running on battery power.
Watching video with the highest settings, there is only the slightest lag, but there is lag. This is a situation where it might bother those who are looking for it, or it might not. It has no effect on typical Office functions, like typing.
We tested using Microsoft OneNote with the iPad acting like a drawing tablet for the Windows device, and while we found that it was possible, it wasn’t as easy as just using the iOS version of OneNote.
In our tests with a 2015 MacBook Pro, we found that Wired XDisplay had less lag than Duet Display. When watching video, synchronization isn’t perfect, but audio is just a hair behind the video. They are so close together that those who aren’t looking for it might not notice. This means that synchronization is more than good enough for typing emails, working in spreadsheets, and similar tasks.
However, we again asked the commercial artist to test whether there is any value in using an iPad Pro to draw directly into Photoshop with XDisplay. When she attempted this, the lag increased dramatically, to the point where lines drawn didn’t appear on the display until about a second after the Apple Pencil had put them on the touchscreen. The artist found this very frustrating.
For comparison, she did the same quick sketch with Photoshop and XDisplay and with Pixelmator, an iOS drawing tool. She found Pixelmator vastly easier to use, and this is reflected in the quality of her sketches, even ones done in just a few seconds.
Air Display 3
At this time, Avatron is still working on support for Windows in the latest version of Air Display, so we were unable to test it with the Surface Pro 2.
Unlike the other applications we’ve profiled here, Air Display 3 supports both wired and wireless connection, but the latter is of limited use. When a MacBook Pro and an iPad Pro were connected over Wi-Fi, the lag was at least a second, and the secondary screen would often freeze, taking several seconds to refresh. This made even using the external screen just for typing emails a frustrating experience.
But when the laptop and the tablet are connected by a Lightning cable, Avatron’s software outperforms any of the rivals we tested. Lag was so short as to be essentially nonexistent.
Air Display 3 has a trick to speed up watching full screen video on the external display: it blanks the main display on the OS X device. This is obviously to allow it to devote more resources to the secondary screen, and it allows video and audio to be almost completely synchronized.
Unlike Duet Display and XDisplay, this Avatron app allows a keyboard hooked to the iPad to be used. This can be a Bluetooth one or the Apple Smart Keyboard.
We once again asked the commercial artist to try sketching in Photoshop with the iPad Air functioning as a drawing pad. In this test, there was so little lag between the Apple Pencil and the on-screen cursor that she judged that Air Display 3 is the only one of these options to she thought she could use on a regular basis.
A feature she would have found very useful has been temporarily disabled for many users, however. Devices running iOS 8 can use pressure-sensitive styli with this software, but not ones running iOS 9.
The latest version of Air Display supports the native resolution of the iPad’s screen, which is 2048 x 1536 on an iPad Pro. Even better, this app can be used to connect to multiple iPads for additional monitors, but we were unable to test this feature.
For Windows users, we recommend Splashtop’s Wired X Display. Not only does it have better performance than Duet Display, it costs less.
Air Display 3 is clearly the best choice for OS X users who want to use an iPad as a second monitor. It’s one of the more expensive options, but it offers the best performance.