Apple released macOS Catalina today, and one of the update’s marquee features is Sidecar, which lets you use your iPad as a second display for your Mac laptop or desktop. The feature is designed to be a handy way to give yourself some extra screen real estate, especially if you regularly carry around both an iPad and an Apple laptop. The Verge’s Dieter Bohn called it his favorite new feature on Catalina in our review.

But there’s a catch if you’re excited to use Sidecar with your laptop: if you’ve been holding out on buying an Apple laptop without the troubled butterfly keyboard, you can’t use Sidecar. According to an Apple white paper, the only laptops that Sidecar works on are:

• MacBooks from 2016 or later (the second generation of Apple’s ultra-thin [and now gone] laptop line)
• MacBook Airs from 2018 or later (Apple’s recent redesign of the MacBook Air)
• MacBook Pros from 2016 or later (Apple switched to butterfly keys in the Pros in 2016)

It’s disappointing to see that Sidecar doesn’t work on any older laptops without the company’s perpetually troubled butterfly keyboard, which has gone through three iterations and is now covered under an extended warranty program Apple launched last year specifically to address the issue for certain models.

But the limited number of supported Macs for Sidecar may in fact be due to chipsets, as Apple’s white paper says the feature requires Intel’s Skylake or newer CPUs. As noted by an astute AppleInsider forums user, Skylake adds support for the HEVC video codec, which suggests the mirroring feature could rely on the codec to share what’s on your Mac’s display with your iPad. We don’t know for sure that’s the case, but it does seem quite plausible.

Apple says Sidecar also works on desktop Macs with Skylake chipsets or newer, including:

• Mac minis from 2018 or later
• iMacs from late 2015 or later
• iMac Pros
• The upcoming 2019 Mac Pro

You’ll also need a relatively new iPad to use Sidecar, too, and it will have to support Apple Pencil. Apple says all iPad Pros are supported, as well as the 6th gen or newer iPad, 5th gen iPad mini, and the 3rd gen iPad Air. And no matter which you use, it will need to be running iPadOS 13.

Update October 7th, 8:25PM ET: Clarified that Sidecar also works on desktop Macs, and added the list of desktop Macs that support Sidecar.