(Pocket-lint) - Apple has confirmed a throttling issue with the new MacBook Pros.

The company released a software update, a supplemental update to macOS High Sierra 10.13.6, which addresses a new bug that causes eighth-generation quad-core and six-core Intel processors in the 2018 MacBook Pro models to unusually throttle.

Here's what you need to know.

What is the MacBook Pro throttling bug?

On July 17, shortly after the first new 2018 MacBook Pros began shipping, YouTuber Dave Lee tested a high-end 2018 15-inch MacBook Pro with 2.9GHz Core i9 chip using Adobe's Premiere Pro. He found that it didn't perform as well compared to a 2017 MacBook Pro with a Core i7 chip. Customers and other media sites soon ran tests and concluded that unusual throttling was affecting their machines' performance.

In other words, Intel Core processors inside new MacBook Pros were throttling - or driving down - to below their base speed.

Why is the MacBook Pro throttling?

It wasn't clear if all 2018 MacBook Pro models were unintentionally throttling due to a bug, but Apple confirmed on 25 July to the media that it found a thermal throttling issue caused by a software bug. There was a missing digital key in the firmware, which subsequently affected the machine's thermal management system and caused clock speeds to drive down under heavy thermal loads.

Apple sent us the following statement, saying it has fixed the issue:

"Following extensive performance testing under numerous workloads, we’ve identified that there is a missing digital key in the firmware that impacts the thermal management system and could drive clock speeds down under heavy thermal loads on the new MacBook Pro. A bug fix is included in today’s macOS High Sierra 10.13.6 Supplemental Update and is recommended. We apologize to any customer who has experienced less than optimal performance on their new systems. Customers can expect the new 15-inch MacBook Pro to be up to 70 per cent faster, and the 13-inch MacBook Pro with Touch Bar to be up to 2X faster, as shown in the performance results on our website."

If you have a new MacBook Pro, then download this new software update: MacOS High Sierra 10.13.6 Supplemental Update. Apple said it is designed to address the issue. 

The software update is exclusive to owners of any 2018 MacBook Pro model. That's every new generation of the MacBook Pro, including both the 13-inch and 15-inch sizes and all the Intel processor configurations. It does not affect previous generations or other Macs.

The new macOS High Sierra update can be downloaded through the Software Update tool in the Mac App Store.

A direct link to download the update is available here.

Want to know more?

See Pocket-lint's handy MacBook guides:

Writing by Maggie Tillman.