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Sonnet eGFX Breakaway Box, First Take: A GPU upgrade path for your Mac

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Apple's World Wide Developer Conference was unusually bountiful this year, offering an assortment of hardware and software updates, as well as previews of forthcoming products such as the HomePod smart speaker and iMac Pro. Somewhat overlooked was the announcement that Metal 2 -- Apple's updated graphics API, due to appear with macOS High Sierra (10.13) later this year -- would support the use of external graphics cards via a Thunderbolt 3 interface.

Macs are often criticized for their poor upgradeability, so this announcement could will be welcomed by the company's professional customers.

Sonnet Technologies isn't the first company to provide an external GPU that can connect to a Mac or PC via Thunderbolt 3 -- companies such as Akitio and Mantiz offer similar upgrade options. However, Sonnet does have a long history of producing upgrade products for the Mac, and its new eGFX Breakaway Box is being used as part of Apple's developer kit for macOS High Sierra, so we were keen to explore the performance improvements that will be available to professional Mac users in the very near future.


Sonnet's Thunderbolt 3-interfaced eGFX Breakaway Box comes with 350W or 550W power supplies, the latter providing extra power to charge the attached laptop.

Images: Sonnet Technologies

Preliminary tests

Comprehensive benchmarking isn't really possible at the moment, as the public beta of High Sierra currently only supports the AMD Radeon RX580 as an external GPU, and with a number of limitations, such as the need to connect the eGFX to a second display when using a MacBook Pro (as we did during our tests).

Even, so the results offer some welcome good news for Apple's professional users. It is possible to use Nvidia graphics cards with the Breakaway Box, using Nvidia's own beta drivers, but that requires some extra hacking, so we stuck with an officially supported Asus RoG Strix RX580 provided by AMD, which costs around £390 (inc. VAT; £325 ex. VAT, or $450).

We tested a Breakaway Box with a 350W power supply, which costs £318 (inc. VAT; £265 ex. VAT, or $299), but there's also a 550W model available for £348 (inc. VAT; £290 ex. VAT, or $349) that can provide extra power to charge a laptop via the Thunderbolt interface. It's a fairly straightforward black metal enclosure, measuring a bulky 205mm high by 185mm wide by 340mm deep, but even then we had to be quite careful squeezing the full-length Radeon card through the side panel and into the single PCI-Express slot housed inside the box.


We tested a Breakaway Box fitted with an Asus RoG Strix RX580 graphics card in its single PCIe slot.

Image: Sonnet Technologies

The beta version of macOS High Sierra currently requires an external monitor to be connected to the Breakaway Box.

Image: Cliff Joseph/ZDNet

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Our 15-inch MacBook Pro recognized the external GPU automatically although, as mentioned, the High Sierra beta currently requires an external display to be connected to the Breakaway Box. This work-in progress arrangement confused our normal Cinebench R15 test software, which resolutely ignored the external GPU for some reason. However, other benchmark apps, such as Geekbench 4.1 and Unigine Heaven were able to switch between GPUs simply by dragging the app's open window from the MacBook's built-in display to our external LG monitor.


Even with a beta OS and drivers, the RX580-equipped Breakaway Box delivered significant performance improvements over the MacBook Pro's internal Radeon Pro 560.

Image: Cliff Joseph/ZDNet

Geekbench 4.1 reported a score of 23,640 using Apple's Metal API on the MacBook's internal AMD Radeon Pro 560, while the RX580 in the Breakaway Box delivered a roughly 30 percent performance increase to 30,600. However, OpenGL performance in Unigine Heaven provided a more substantial increase. Using Heaven's highest 'Ultra' quality setting at 1920-by-1080 (full HD) resolution, the MacBook Pro's native GPU managed a mere 16fps, but almost doubled this to 31fps when using the Breakaway Box.

Sonnet claims to have achieved frame rates around 55fps using Nvidia's GeForce GTX 1060 cards, so professional Mac users can certainly look forward to significant performance improvements once High Sierra get its final release.

Of course, the Breakaway Box does add some £300 to the basic cost of whatever graphics card you choose, but using an external enclosure has other advantages too. It can easily be shared by several users in an office -- who can then argue over whose deadline is most important. The Breakaway Box isn't limited to just GPUs either, as you could swap in alternatives, such as high-end audio cards, which could be useful for small studios needing to work with a range of multimedia applications.

Sonnet has also indicated that High Sierra will allow the Breakaway Box to work with older Macs featuring Thunderbolt 2, with only a minor performance penalty. That would certainly be an enticing and cost-effective option for existing Mac users -- although it is, of course, subject to confirmation with the final release of High Sierra.



Image: Sonnet Technologies

If nothing else, the arrival of macOS High Sierra will be welcomed by Apple's professional users if it finally allows them to make use of graphics upgrades such as Sonnet's eGFX Breakaway Box.

Even using the beta OS and currently available drivers, the Breakaway Box delivers significant performance improvements for Apple's current professional Mac models. It's not cheap, but it's still far cheaper than buying a brand-new Mac -- which has been Apple's only upgrade path since the company discontinued its old Power Mac tower systems way back in 2006.

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Packaged Quantity 1
Power Device
Type power adapter
Power Provided 500 Watt
Nominal Voltage AC 110/240 V
Frequency Required 50/60 Hz
Interface Provided
Type Thunderbolt 3
Qty 1
Environmental Parameters
Min Operating Temperature 32 °F
Max Operating Temperature 95 °F
Manufacturer Warranty
Service & Support Limited warranty - 1 year
Type 1 year warranty
System Requirements
OS Required Apple macOS Sierra 10.12.6 or later, Windows 10 64-bit Edition
Brand Sonnet
Product Line Sonnet eGFX
Model Breakaway Box 350
Packaged Quantity 1
Device Type system bus extender
Dimensions & Weight
Width 7.3 in
Depth 13.4 in
Height 8 in
Weight 7.05 lbs
Audio Output
Type none
Expansion Bays
Type none
Physical Characteristics
Weight 7.05 lbs
Expansion Slots
Type PCI Express 3.0 x16
Form Factor full-length, full-height
Total Qty 1
Free Qty 1
Slot Comments x4 mode
Slot Required
Type none
Cable Details
Type Thunderbolt cable
Form Factor external
Included Qty 1
Length 1.6 ft
Service & Support
Type 1 year warranty
Service & Support Details
Type limited warranty
Full Contract Period 1 year