Looks like no one’s replied in a while. To start the conversation again, simply ask a new question.

2020 iMac: external start up with High Sierra?

Setting up my new 2020 27" iMac with catalina, and am hoping to occasionally use an external SSD, a copy of my previous High Sierra iMac, so can run older programs (looking at you Adobe). Possible?

Thanks! John

Posted on Aug 21, 2020 3:57 PM

Top-ranking reply

dialabrain

Level 10

124,691 points

Posted on Aug 21, 2020 4:12 PM

No.. High Sierra nor Mojave will boot on an iMac that shipped with Catalina.

View in context

Similar questions

How to install HighSierra on to an external drive I have a recent MacBook Pro with Big Sur installed. I cannot read older CDs with that configuration. Some time ago I discovered that if I ran the computer using an external hard drive with High Sierra installed I could read them. However, I can't start up from that installation. I can't get a copy of High Sierra from the App Store because it thinks I want to install it on my computer. I just need the installation disk to install it on the SSD hard drive. Where do I find that?
341 3
Run Photoshop CS3 from SSD External Hi, I recently bought an M1 Mac. I realise that I cannot run Photoshop CS3 on this machine. However, could I install High Sierra and CS3 on an external SSD and then thunderbolt this SSD into my M1 Mac and boot to the SSD for when I need to use Photoshop. Many thanks for any help, James
448 5
External drive, bootable to Mavericks, 32 bit In addition to my main drive, I have an external drive that is bootable to Mavericks. I have this set up so that I can run my still-functional Adobe CS 5.5. Current OS on my main drive is 10.14.6 Mojave. If I upgrade to Catalina, will that have any effect on my external drive running 32-bit Adobe software. Wouldn't think so, but I thought I'd ask.
185 3

1 reply

Top-ranking reply

dialabrain

Level 10

124,691 points

Aug 21, 2020 4:12 PM in response to John Phillips10

No.. High Sierra nor Mojave will boot on an iMac that shipped with Catalina.

2020 iMac: external start up with High Sierra?

Welcome to Apple Support Community

A forum where Apple customers help each other with their products. Get started with your Apple Account.

Learn more Sign up