Back To Earlier OS

[hughvane]

I’ve bought a late 2012 iMac i7/27” operating Catalina which - if I have read correctly - is the first of the MacOS 64-bit. All my other Macs operate earlier 32-bit OS versions.

Given that this iMac must have been issued originally wth 32-bit architecture, is it possible for me to go back to Mojave, for example, so I can utilise the significant quantity of earlier apps and games?

 

[pigoo3]

You can run any macOS on this 2012 27" iMac from macOS 10.8 "Mountain Lion" thru macOS 10.15 "Catalina".

Mojave is macOS 10.14...thus no problamo.

HTH,

Nick

 

[Rod]

Going back to an earlier version of Mac OS can be tackled in two ways.

The simplest was I can think of would be to Reinstall the OS the device shipped with from the using Shift - Option - ⌘ - R at boot. This is designed to install the original macOS the device shipped with.
From there you can upgrade the OS by downloading the installer from How to get old versions of macOS
The only catch with this is the installer can sometimes default to network recovery which can be problematic. Dropping out, can't connect etc.

The second method is to download the installer for the macOS you choose eg. Mojave the last macOS that can run 32bit apps.
Create a Bootable macOS Installer using a 3rd party app like Install Disk Creator onto a thumb drive.
Boot your device from the thumb drive and use it's version of Disk Utility to erase your device's internal HD and install a mint version of Mojave (if you choose that OS).
This will ensure there is no "rubbish' on your device and it will start up with the Setup Assistant allowing you to set all your own system preferences from scratch.

 

[hughvane]

I should have made myself clearer in my OP.

The iMac is on Catalina, which will not tolerate 32-bit apps, therefore I wish to downgrade (as it were) to Mojave. I tried the Apple source, but once loaded (other than in the Dock, where does it go?), I then received the message you see in the attachment.

From Rod's post, do I understand correctly that somewhere on the iMac's HD there lurks an installer for Catalina?

If I feel an onrush of bravery sufficient to try Method 2, I have heaps of either thumb drives, or portable HD, that could do the job.

 

[chscag]

You can not install Mojave over Catalina. The system won't allow an older version of macOS to be installed over a newer version.

Your best bet is to follow Rod's instructions and make a thumb drive installer. Note what he said about erasing the drive.

 

[hughvane]

Help me understand, please: what is it in/about Catalina (64-bit) that is incompatible with an earlier OS, eg. Mojave (32-bit); and why is it blocking/preventing a 32-bit OS (2012, 10.8.2) that shipped with the iMac in the first place?
[Note: I did not install Catalina, that was done by the previous owner of the iMac.]

 

[IWT]

Help me understand, please: what is it in/about Catalina (64-bit) that is incompatible with an earlier OS, eg. Mojave (32-bit); and why is it blocking/preventing a 32-bit OS (2012, 10.8.2) that shipped with the iMac in the first place?
[Note: I did not install Catalina, that was done by the previous owner of the iMac.]

Hugh; nobody is saying that your Mac is incompatible with an earlier OS. In fact, Nick said "You can run any macOS on this 2012 27" iMac from macOS 10.8 "Mountain Lion" thru macOS 10.15 "Catalina".

To put it another way: your Mac likely shipped with Mountain Lion. The previous owner(s) upgraded to Catalina, either as each new OS came on stream, or maybe every few years - who knows?

Fact is, you have a workable Mac and if you need to run 32bit apps, no problem. You wipe the Hard Drive (essential) and then install whoever OS suits you, Mojave being a good choice as it's the most recent OS to run 32bit apps.

There is nothing complicated about what you seek - a competent OS running 32bit apps, and Mojave fills the bill exactly.

Rod spelt out two means of achieving this. I'd probably use the second one. But to be absolutely clear - to install any previous OS, you must wipe/erase the current Hard Drive before you can install another one.

HTH

Ian

 

[Randy B. Singer]

Help me understand, please: what is it in/about Catalina (64-bit) that is incompatible with an earlier OS, eg. Mojave (32-bit); and why is it blocking/preventing a 32-bit OS (2012, 10.8.2) that shipped with the iMac in the first place?

These articles may help you to understand:

How to downgrade to an earlier version of macOS - ChrisWrites.com

Reverting to an earlier version of macOS isn’t as easy as selecting an option from a menu, or downloading the earlier release and then reinstalling it

www.chriswrites.com

How revert a macOS update: switch back to Ventura from Sonoma

Regret updating to Sonoma or having problems with the current version? Here's how to uninstall Sonoma and revert to an older version.

www.macworld.co.uk

How to reinstall macOS - Apple Support

You can use macOS Recovery, your computer's built-in recovery system, to reinstall the Mac operating system. Reinstalling macOS doesn't remove your personal data.

support.apple.com

Create a bootable installer for macOS - Apple Support

Use an external drive or secondary volume as a startup disk from which to install macOS.

support.apple.com

 

[pigoo3]

Help me understand, please: what is it in/about Catalina (64-bit) that is incompatible with an earlier OS, eg. Mojave (32-bit); and why is it blocking/preventing a 32-bit OS (2012, 10.8.2) that shipped with the iMac in the first place?
[Note: I did not install Catalina, that was done by the previous owner of the iMac.]

Downgrading the macOS is not an easy process...or even installing an older macOS version no longer directly available via the Apple Store.

If an older version of the macOS is needed...you're actually not really downgrading the macOS...you're reinstalling the macOS. It's pretty much as "nuke & pave" approach.

Now here's an "advanced idea" for you. There may be times having Catalina installed could be beneficial...and then there may be times having Mojave installed could be beneficial.

If this sounds interesting...here's what I would suggest...create a 2nd APFS volume for a Mojave install. Then you'd have both Catalina & Mojave at your disposal. To switch between the 2 you do need to reboot the computer (not too much of an inconvenience to easily have access to two different macOS versions):

Partition a physical disk in Disk Utility on Mac

In Disk Utility on your Mac, add, delete, erase, or enlarge a partition on a storage device.

support.apple.com

Think of this "2nd APFS volume" as being similar to what in the "old days" we used to call partitioning a hard drive.

One big difference with additional APFS volumes is...the full storage capacity of the drive is available to all AFPS volumes (where in the old days with partitioning a hard drive...you had to decide what size partition to make...and then that partition was limited to that amount of storage on the drive).

As far as installing Mojave. As others have already suggested...definitely go the bootable USB thumb drive route. This bootable installer will come in handy now...and later should you need to do this again on the same computer or a future computer.

Regarding how to make the bootable macOS thumb drive. A lot of procedures on the internet have you using the Terminal App (which not everyone is comfortable with). There's an app that makes this process much easier (once you have the Mojave install file)...called "DiskMaker X" (makes things easier without needing to use Terminal)...free as well:

Downloads

diskmakerx.com

As I mentioned..."downgrading" the macOS on an Apple computer is not easy. But once you understand what needs to be done...it's really not super-bad. But it will take some time...thus set aside a block of time for this...and all should go well.

Nick

 

[ferrarr]

You want to use Internet Recovery. See this document;

If you can't start up from macOS Recovery - Apple Support

Learn what to do if you can't get your Mac to start up from macOS Recovery.

support.apple.com

Now known as macOS Recovery over the internet.

 

[hughvane]

If this sounds interesting...here's what I would suggest...create a 2nd APFS volume for a Mojave install.

You bewdy! It's my age, I swear it, but I forgot I had done partitioning with my old(er) Mini, which has two partitions, one with SLpd, the other with (does a quick check) El Capitan. Either partition works as it should.

From your advice I'm surmising that I can partition the iMac's (SATA) HD into two partitions: one with 32-bit Mojave, the other (existing) with 64-bit Catalina. Is that correct, and will one HD cope with two different OS 'bit' architecture (whatever the correct term is)?

That raises the question of Disk Utility, and how it might, under 64-bit, respond to being required under Catalina to format a partition with 32-bit Mojave.

Further advice please ..... Hugh

 

[Slydude]

Others may chime in with additional information but here are my thoughts:

You should be able to do what you propose with two different partitions. I did this for a while on a backup of my iMac until I got a second backup drive. Disk Utility shouldn't have a problem setting that up.

Someone else can clarify one thing for you: You may have to avoid formatting the drive as APFS. I don't remember if the OS versions that support 32-bit apps also support APFS formatting.

 

[MacInWin]

Someone else can clarify one thing for you: You may have to avoid formatting the drive as APFS. I don't remember if the OS versions that support 32-bit apps also support APFS formatting.

To make it even more challenging, the drive will need to be partitioned into two, one for Mojave and one for Catalina. Catalina will need APFS formatting on that partition, Mojave can use HFS+. Of course, doing this partitioning will erase the entire drive, so backups will be critical unless it's OK starting from scratch on both.

 

[hughvane]

To make it even more challenging, the drive will need to be partitioned into two, one for Mojave and one for Catalina. Catalina will need APFS formatting on that partition, Mojave can use HFS+. Of course, doing this partitioning will erase the entire drive, so backups will be critical unless it's OK starting from scratch on both.

I'm even more confused (and frightened) by reading this, which appears to contradict what is being promoted from expert replies, ie. HFS+ vs APFS.
Mac OS Extended VS APFS - Mac Research

The first I thought I was familiar with as I'd used it to partition the older Mini HD into SLpd and El Capitan (both being 32-bit), but now I'm beginning to wonder if in fact I used APFS. Heeeeeelp!

Erasing everything that is currently on the iMac HD will not matter, as I can reload third-party material from the internet, but when reinstalling the two OS - should I decide to do that - I presume I will be provided with all the software that goes with the pertinent OS.

 

[chscag]

I'm even more confused (and frightened) by reading this, which appears to contradict what is being promoted from expert replies, ie. HFS+ vs APFS.
Mac OS Extended VS APFS - Mac Research

What's confusing about that article? It spells things out very well.

The first I thought I was familiar with as I'd used it to partition the older Mini HD into SLpd and El Capitan (both being 32-bit), but now I'm beginning to wonder if in fact I used APFS. Heeeeeelp!

Not possible as both Snow Leopard and El Capitan would not install or even recognize an APFS formatted drive.

Erasing everything that is currently on the iMac HD will not matter, as I can reload third-party material from the internet, but when reinstalling the two OS - should I decide to do that - I presume I will be provided with all the software that goes with the pertinent OS.

Yes, depending on which version of macOS you decide to install.