Apple will release its first Mac powered by an ARM processor in 2021, Bloomberg reports. The company is thought to have three Mac processors in development as part of its Kalamata project, which are all based on the A14 chip that’s due to be used in this year’s flagship iPhone lineup. According to Bloomberg, the first of these processors will include a 12-core CPU with eight high-performance “Firestorm” cores and at least four energy-efficient “Icestorm” cores.

Apple has long been rumored to be developing its own in-house ARM processors to replace the Intel chips it currently uses in its Macs. Rumors of the switch date back to at least 2012, and since then, we’ve heard multiple rumors that Apple could release its first ARM-powered Mac in 2020 or 2021. Although this latest report corroborates a recent report from analyst Ming-Chi Kuo that suggested an ARM Mac could come in 2021, there’s a chance the ongoing COVID-19 pandemic could force Apple to delay its plans.

The switch would give Apple much more control over its own hardware at a time when Intel has been struggling to offer significant performance increases with each new generation of hardware. Current ARM processors are also often more power-efficient, which helps with battery life. Switching to ARM is expected to let Apple reduce its processor costs by 40 to 60 percent.

Bloomberg’s report offers a lot of technical details on the form Apple’s chips could take:

Three Mac System-on-Chip (SoC) designs based on the A14 processor are currently in development, and work has also started on a Mac SoC based on next year’s iPhone processor. Bloomberg speculates that Apple is planning to keep both its laptop and mobile chips on the same development cycle.

The Mac chips will reportedly be manufactured by TSMC based on a 5nm fabrication process.

The first of these chips will feature eight high-performance CPU cores and at least four energy-efficient cores, for 12 cores in total. The A12Z chip used in the current iPad Pro has eight cores: four high performance and four energy efficient.

As well as a CPU, the SoC will also include a GPU.

ARM Mac computers will continue to run macOS rather than switching to iOS, similar to the approach taken with existing Windows laptops that use Qualcomm ARM processors.

Bloomberg speculates that Apple’s first ARM-based machines will be lower-powered MacBooks because its own chips won’t be able to match Intel’s performance in its higher-end MacBook Pros, iMacs, and Mac Pro computers.

Back in 2018, Apple reportedly developed a prototype Mac chip based on that year’s iPad Pro A12X processor. The success of this prototype is thought to have given the company the confidence to target a transition as early as 2020.

The big question is how well the first- and third-party macOS software will run on the new hardware architecture since software compatibility has been a pain point for Windows laptops running on ARM. Regardless, the shift will be the biggest change for the MacBook lineup since it announced a switch to Intel’s processors back in 2005.