Everyone gets excited about the iMac Pro’s multi-core functionality, and rightfully so. Having applications like Final Cut Pro X and Screen Flow 7, apps that take advantage of multiple cores to speed up work, can have major performance implications. Another speed-oriented iMac Pro feature can make a noticeable difference in certain workflows as well.

One of the more unheralded new additions to the iMac line is support for UHS-II SD Cards. It means that users may experience noticeably faster file transfer speeds when offloading photos and video footage to the iMac Pro from supported cards.

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UHS-II stands for Ultra High Speed Class II, these cards employ a second set of contacts that make them easy to distinguish from slower cards. UHS-II readers would therefore need to be able to read this second row of contacts in order to take advantage of the speed increase. The iMac Pro is the first Mac computer with the needed hardware capable of reading UHS-II SD Cards.

Like standard SD Cards with a single set of contacts, there are different speeds within the UHS-II speed class, so the actual performance of your card will vary depending on a variety of factors. I opted for a Sony G Series SDXC UHS-II card, but there are several available to choose from.

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UHS-II may not mean much to you if you rarely use SD Cards, or if you only use them to import compressed photos. But if you’re working with RAW photos, or extremely large video files, these cards can save you time during the import process.

I shoot video on Canon and Panasonic cameras. While the video bitrates that I currently use on these cameras is relatively low, I tend to keep my camera rolling for extended periods of time, resulting in huge files. For example, one 17 minute 15 second video that I recently shot was 19.64 GB — roughly 150Mb/s.

While that may not seem like a huge file, when transferring that sort of data from slower UHS-I cards, the time it takes to complete the transfer can quickly add up. For example, it takes around 4 minutes 51 seconds to transfer that 19.64GB file from my PNY Elite Performance (95 MB/s rated) SDXC Class 10 SD Card to my Mac via Final Cut Pro X. That’s the equivalent of roughly 69MB/s. Transferring that same file via Final Cut Pro X using the UHS-II card yielded a total transfer time of 1 minute 50 seconds, or 183 MB/s.

In the Final Cut Pro X comparison above, If you import 5 files of a similar size every week, you’d be saving roughly 15 minutes a week on import times. When you scale that up for the whole year, you’re looking at nearly 13 hours of time saved on imports, a not so insignificant number.

UHS-II-compatible SDXC cards



Sony G Series 64GB
Sony G Series 128GB
SanDisk Extreme Pro 64GB
SanDisk Extreme Pro 128GB

Final Cut Pro X adds overhead to file transfers, however. Transferring the same file directly to the Desktop folder via Finder yielded 3 minutes 29 seconds for the UHS-I card, and 1 minute 9 seconds for the UHS-II card. Those readings trend closer to the “up to” speeds found on product marketing materials.

It’s also worth noting that the Sony G Series card is faster than the two UHS-I cards that I tested, even when not connected to a UHS-II compatible reader. But without the faster reader, the speed differences may not be enough to warrant the price premium demanded by UHS-II cards.

And what if you don’t own an iMac Pro, but want to take advantage of UHS-II? You can still save time by bypassing your computer’s built-in SD Card reader, and purchase an external USB 3 SD Card reader with support for UHS-II cards.


This is obviously not a scientific test by any stretch of the imagination, but it should give you a rough idea of the benefits provided by UHS-II.

If you regularly transfer large video files from an SD Card to your iMac Pro, it may be a good idea to invest in UHS-II cards going forward. Yes, these cards cost substantially more, but the time saved may help offset the cost over the long term, while removing another bottleneck in your workflow. Much will depend on the amount of data you regularly transfer along with your specific video process.

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