Will ARM-based Apple Silicon Macs run the macOS or iOS? What version?

ARM-based Apple Silicon Macs initially ran macOS Big Sur (macOS 11). As of the date last updated, all are capable of running macOS Monterey (macOS 12), macOS Ventura (macOS 13), and macOS Sonoma (macOS 14), as well. These Macs do not boot the iOS, but they are capable of running iOS apps written for the iPhone and iPad unmodified (unless the developer opts-out).

Better developers likely will customize their iOS apps to "feel" a bit more "Mac-like" on the macOS, but iOS apps inevitably will be the primary focus going forward.

Photo Credit: Apple, Inc. (macOS Big Sur)

Will existing Mac apps run on ARM-based Apple Silicon Macs? Will they be faster or slower?

Post-Release Update: The initial consumer release of Apple Silicon Macs on November 10, 2020 -- a 13" MacBook Air, 13" MacBook Pro, and Mac mini -- delivered enough of a performance boost over their Intel-based predecessors that even apps running via Rosetta 2 commonly were faster, or at least not significantly slower. An impressive improvement compared to the developer only Mac mini DTK available prior to the public models and referenced in the speculative answer below.

If recompiled as a "Univeral 2" binary, many existing Mac apps will be able to run on ARM-based Apple Silicon Macs natively at the same speed.

Many 64-bit macOS apps written for Intel processors also will run on ARM-based Apple Silicon Macs courtesy of the Rosetta 2 translation engine (exceptions below). However, Apple rather coyly notes in developer docs that "the translation process takes time, so users might perceive that translated apps launch or run more slowly at times."

It would be reasonable to expect apps running through any type of emulation, virtualization, or translation process to be slower than native apps. No formal information is available, but reasonable speculation can be made to guess how much slower using leaked Geekbench 5 benchmarks about the Mac mini DTK available for developers compared to the similar iPad Pro (2020) models.

Compared to the iPad Pro (2020) lineup running native code, the Mac mini DTK is around 26% slower in single-core tasks and 38% slower in multicore tasks running the Geekbench 5 benchmark via Rosetta 2.

It is worth noting that the Mac mini DTK is downclocked compared to this iPad Pro and is running beta software that is not optimized. It's not a truly direct comparison, either, because the iPad Pro is not running the same operating system, but if we assume an equal clockspeed and some further software optimization before final hardware is released, it would not be unreasonable to expect software running via Rosetta 2 to be in the neighborhood of 20%-30% slower than native apps running on the same Mac.

It also is notable that neither of these devices are using the latest Apple processors. It is a safe bet that the initial consumer release of ARM-based Apple Silicon Macs will have faster processors, perhaps even fast enough to deliver performance via Rosetta 2 that could equal many Intel-based Macs released a year or two earlier.

What is "Universal 2"? What is a universal binary?

In basic terms, a universal binary is an application that runs on multiple platforms.

Apple originally used the term "universal" to refer to software that ran on both PowerPC and Intel Macs. In the case of "Universal 2", Apple explains that it is an app that runs on both Intel-powered and Apple Silicon Macs:

A universal binary runs natively on both Apple silicon and Intel-based Mac computers, because it contains executable code for both architectures.

This process should be nearly seamless for the end user, but it is worthwhile to keep in mind that a "Universal 2" app will be faster on Apple Silicon Macs than one running via Rosetta 2.

What is "Rosetta 2"? What does it support?

In a nod to the original Rosetta -- which made it possible to run software written for PowerPC-based Macs on Intel-based Macs -- Rosetta 2 makes it possible to run software written for Intel-based Macs on ARM-based Apple Silicon Macs.

In developer documentation, Apple more specifically explains:

Rosetta is a translation process that allows users to run apps that contain x86_64 instructions on Apple silicon. . .

To the user, Rosetta is mostly transparent. If an executable contains only Intel instructions, macOS automatically launches Rosetta and begins the translation process. When translation finishes, the system launches the translated executable in place of the original.

Apple further notes that Rosetta 2 "can translate most Intel-based apps, including apps that contain just-in-time (JIT) compilers," but it does not work with apps that include or interact with:

• Kernel extensions
• Virtual Machine apps that virtualize x86_64 computer platforms
• Some newer instruction sets and processor features, such as AVX, AVX2, and AVX512 vector instructions

In basic terms, Rosetta 2 likely will work well, or well enough, with the majority of mainstream productivity apps, but is more likely to not work with software that interacts more directly with the operating system, hardware, or graphics hardware.

In particular, those with mission critical needs involving virtualization or high-end graphics, video, or scientific applications likely will want to wait until native software is available before considering an upgrade to ARM-based Apple Silicon Macs.

Will ARM-based Apple Silicon Macs be able to boot Windows? Run Windows under virtualization or emulation?

In an interview with Daring Fireball's John Gruber, Apple SVP Craig Federighi affirmed that "we're not direct booting an alternate operating system" like Windows on ARM-based Apple Silicon Macs.

There is a version of Windows 10 for ARM processors, but without an official blessing from Apple (and perhaps Microsoft, as well), it is a safe bet that there will be technical, and potentially legal, roadblocks to booting Windows on ARM-based Macs. Clever hackers were able to boot Windows on Intel-based Macs when they were not supposed to; booting Windows on an ARM-based Mac likely is not outside of the realm of possibility, but it would seem to be exceedingly difficult with Apple controlling the hardware so tightly.

Parallels Desktop and VMWare Fusion created for Intel-based Macs cannot run on ARM-based Apple Silicon Macs because the Rosetta 2 environment does not support Virtual Machine apps. However, Apple demonstrated an early native version of Parallels Desktop on the Mac mini DTK developer box at the WWDC 2020 event and it was all but certain that it would be possible to run other operating systems on ARM-based Apple Silicon Macs via virtualization apps like Parallels Desktop and VMWare Fusion in the future.

Subsequently, Parallels has released versions of Parallels Desktop for Mac which support Apple Silicon Macs. VMWare has released VMWare Fusion for Apple Silicon Macs, as well. Microsoft now formally supports Windows running on Apple Silicon Macs via virtualization, also.

Microsoft also has introduced Windows 365 Cloud PC, which reportedly securely streams "the full Windows experience -- including all your apps, data, and settings -- to your personal or corporate devices" including Apple Silicon Macs. For users without high end technical needs, this cloud option may make virtualization or native booting unnecessary entirely.

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