Apple doesn’t support macOS downgrades on their hardware, because macOS updates often incorporate firmware updates, and there’s no guarantee of backwards compatibility in those either.
This almost never comes up, because they typically don’t need to break things, but I can absolutely envision them performing microcode updates that make the CPU incompatible with previous releases.
They owe nothing to anyone regarding these instructions, and they will act accordingly. That’s what unsupported means here: not the PC or Android meanings where everyone has to kludge it in, but the Apple meaning where they will release without warning an OS point release version 15.2.7 that shatters an entire ecosystem built on unsupported APIs.
These instructions are just unsupported APIs in Silicon. Use them at your peril.
Maybe but if your encoder runs twice as fast, or your game physics can handle twice the amount of objects, or your renders take half the time, you can bet vendors world at least provide unsupported patches of their software. If we don't see this in the wild, I'll be shocked.
The same vendors that can’t be bothered to port their software to a macOS released in the past three years, require us to run 32-bit apps for plugins and DRM dongles, and refuse to implement platform-native Metal in games because twice the performance of OpenGL isn’t worth it to them since they perceive Macs as being slow?
Somehow I doubt it. But hey. Maybe M1 will change their minds. Maybe something more powerful will. A 27” iMac that can play FPS games at 60fps/5K/HDR with virtual Atmos surround out of the box? Near-effortless console porting to a future Silicon AppleTV, with gameplay compatibility across both devices? They’ll realize what they’re missing out on eventually :) But they’re not going to code M1 assembler until they do, and it’s easier for them to use Apple’s frameworks than play games with the CPU.
(Yes, ffmpeg will probably do this. Good for them! And I’m sure Adobe will give it serious consideration - and then reject it, since it would get their apps rejected from the app stores and harm their relationship with Apple.)
First, let's leave games aside, because Mac isn't a profitable target for game publishers. Same with engineering. As for 3d rendering, video editing, compositing though, there's some scope for Mac to reclaim lost market share.
> it’s easier for them to use Apple’s frameworks than play games with the CPU
The things I'm talking about are broader than what their accelerated libraries support. Matrix operations are ubiquitous across heavy-weight computation, including stress analysis, physics simulation, machine learning, video and sound processing, compression, ray-tracing.. why would Apple limit their market? There's a whole host of 3rd party applications that would be augmented with this co-processor. And it should be trivial to add a compiler intrinsic that compiles to some bitcode primitive that can ensure it works across all devices and OS's... or just provide a mechanism to detect the extension.
> And I’m sure Adobe will give it serious consideration - and then reject it, since it would get their apps rejected from the app stores and harm their relationship with Apple.
This is bad for Apple. And bad for the consumer. Final Cut Pro isn't the only tool that video professionals need to use, and you can bet FCP will be using the coprocessor directly under the hood.
> Matrix operations are ubiquitous across heavy-weight computation, including stress analysis, physics simulation, machine learning, video and sound processing, compression, ray-tracing.. why would Apple limit their market?
Apple offers frameworks that accelerate the relevant operations, and has over time shown an ongoing willingness to limit their market, even when that’s seen as unpalatable or unprofitable or unhelpful to themselves or their users. I assume that the frameworks offering acceleration will expand their uses somewhat over time. I expect those frameworks to be the only compelling solution for having portable matrix acceleration across the complete spectrum of Apple Silicon hardware revisions over time, especially if Apple revises their undocumented operations and updates their frameworks annually (which they can easily do, since each year’s hardware release already demands the latest macOS to boot at all).
You can, but the older version of macOS has to be new enough to support the hardware you're running, and it has to be compatible enough to allow booting.
In general, the oldest macOS you can boot on any given Mac is "the version the Mac shipped from the factory with". So, for example, the 2017 iMac Pro can't boot a 2016 or earlier macOS.
This is still unsupported, mind you — if your 2017 iMac Pro is firmware updated to 2020 and you're booting a macOS from 2018 on it, you may encounter random bugs and/or crashes and/or mysterious issues due to assumptions made by the older macOS that are no longer entirely valid on 2020 firmware — but in general, it should work as long as the macOS is newer than the hardware.
(You probably won't be able to boot an M1 macOS external drive on an Intel Mac, and vice versa, for other reasons unrelated to this. In that scenario, Migration Assistant is probably your only choice anyways.)
I use Mavericks because I like Mavericks, and a few months ago I discovered something bizarre: the mere act of booting a Mavericks installation USB on my 2014 Macbook Air appears to wipe the hard drive. As in, I'm not running the installer and I'm not opening Disk Utility, I'm merely telling the computer to to boot from the USB key. It seems that by the time I've reached the language select screen, the internal hard drive's filesystem is toast.
I did this several times because I couldn't believe what I was seeing. I can't say for sure where the source of the problem lies—maybe something is weird with my installation media—but my theory is that a firmware and/or microcode update subtly broke something in Apple's old installers, possibly when they added APFS support. I looked into downgrading the firmware, but it seems to be impossible from what I can tell[1].
Mind you, outside of this one quirk the OS and installer run fine.
Oh, yes, nothing important! Not only do I keep lots of backups, but the laptop is very much a secondary machine to my desktop, especially in the age of COVID. All I lost was the few hours it takes to reinstall my apps and such. :)
No M1 Mac can boot any OS prior to Big Sur - there simply isn't any binaries for it to run.
With intel macs you can boot and install older macOS's up to a certain point. Like the previous poster says, it's about what firmware versions you have.
For example, if your mac came with Sierra, and through the regular usage and update, you patched it up to Mojave, and installed (or was forced to install by the way, there is no way to reject certain types of updates) firmware updates, you find that all of a sudden you can't re-install Sierra anymore. You'd need to install whatever version your firmware now supports.
This behaviour is undocumented and it's case by case - for each mac hardware there is a firmware for it - there are lots of people online who have figured out patch levels are for each revision of hardware, etc - but it's more trial and error to see what older version of macOS you can downgrade to.
> For example, if your mac came with Sierra, and through the regular usage and update, you patched it up to Mojave, and installed (or was forced to install by the way, there is no way to reject certain types of updates) firmware updates, you find that all of a sudden you can't re-install Sierra anymore. You'd need to install whatever version your firmware now supports.
I have never seen any record of this happening. I'm really quite sure you've always been able to install the earliest OS that your model of Mac shipped with.
The odd situation I mentioned above is the closest I've ever seen to a firmware update causing problems (if that's even the cause), and even then the OS runs fine.
Yah even if it hasn't happened to you yet, be aware that this is something that happens.
There actually is a table of firmware versions, etc - once you upgrade your old Mac hardware past a certain firmware, you will no longer be able to run certain versions of macOS "before" the firware was supported.
This isn't just between "major" versions, also between "minor" versions of macOS
For example, between the current version of macOS Sierra, which is on 10.12.6 (6 being the minor version), if you try to install for example 10.12.x where x is below 6, etc - you might get the infamous ? or the circle with a slash through it on bootup.
...Wait, no, I can't say for sure if I'd ever run 10.12.6 specifically. But I ran stock Sierra (10.12.0) after running Mojave, and it's hard to imagine that would result in a more compatible firmware...
This almost never comes up, because they typically don’t need to break things, but I can absolutely envision them performing microcode updates that make the CPU incompatible with previous releases.
They owe nothing to anyone regarding these instructions, and they will act accordingly. That’s what unsupported means here: not the PC or Android meanings where everyone has to kludge it in, but the Apple meaning where they will release without warning an OS point release version 15.2.7 that shatters an entire ecosystem built on unsupported APIs.
These instructions are just unsupported APIs in Silicon. Use them at your peril.