Running Catalina of External HD

[thewall]

I have a late 2014 iMac currently running Big Sur, i upgraded from Catalina but some of my 3rd party apps don't work which i do need, is it possible to download Catalina and put it on an external HD so i could boot up the Mac using that Hd so i can us my apps.

 

[Fishrrman]

Yes, you can boot and run Catalina from an external drive.

BUT... WARNING...
You DO NOT want to try this with a platter-based hard drive.
It will "run"... but the "running" will seem more like "walking".

USE AN SSD.
(consider yourself as having been duly warned by reading this post)

 

[thewall]

Thanks for the info Fishrman how would i go about getting Catalina onto a SSD

 

[Fishrrman]

"how would i go about getting Catalina onto a SSD"

I think you'll need to:
1. Download Catalina from Apple's servers
2. Create a bootable USB installer
3. Boot from the USB installer
4. Install Catalina to the SSD
5. Set it up with an account, apps, etc.

Try here to download Catalina:

‎macOS Catalina

‎macOS Catalina gives you more of everything you love about Mac. Experience three all-new media apps: Apple Music, Apple TV, and Apple Podcasts. Locate a missing Mac with the new Find My app. And now coming to Mac, your favorite iPad apps. You can even extend your desktop using iPad as a second...

apps.apple.com

For creating the USB installer, I would suggest either:
- Diskmaker X
or
- Install Disk Creator.
Both are FREE.
Try one, if the first one doesn't work, TRY THE OTHER ONE.
MAKE SURE you download the right version of either of these for use with Catalina.

 

[thewall]

Thanks 😀

 

[Dave Braine]

Why create a bootable USB installer? Why not run the installer on the iMac and just chose the SSD as the drive to install on?

 

[HDFan]

Why not run the installer on the iMac and just chose the SSD as the drive to install on?

Yep.