El Capitan & Catalina on Same External Drive?

Question

Level 1

82 points

El Capitan & Catalina on Same External Drive?

I have a 2015 MacBook Pro upon which I am currently running El Capitan on the internal SSD. I want to stick with El Capitan for the time being. This machine is capable of running Catalina as well.

Is there any way I can have both operating systems on an external SSD or flash drive and if so would running from Catalina form the external alter in any way anything that is on the internal SSD of the laptop running El Capitan?

If I can set up an external drive to handle both OSs how would I go about doing that?

MacBook Pro 15", macOS 10.14

Posted on Mar 28, 2020 5:21 PM

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Answer 1

Lanny

Level 6

13,225 points

Mar 28, 2020 5:33 PM in response to Russ G

Buy an external large enough to be partitioned into two. Install El Capitan on one partition and Catalina on the other. However, an external SSD will have noticeably slower performance than an internal SSD. You should consider getting a larger internal drive that could be partitioned suitably. Besides, using a portable tethered to an external drive kind of defeats the purpose of having a portable in the first place.

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Answer 2

Lanny

Level 6

13,225 points

Mar 28, 2020 6:38 PM in response to Russ G

Partition the drive into 2 HFS+ partitions. Once done use the Erase option to turn one into a APFS partition. Or just install Catatlina on one of them and it will convert the partition to APFS before the install.

Try using the Disk Utility Help screens:

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Answer 3

Russ G Author

Level 1

82 points

Mar 28, 2020 5:42 PM in response to Lanny

Thanks. Maybe my question wasn't as clear as need be. Catalina and El Capitan require different file formats APFS and HFS+ respectively. Can an external drive have dual file formats and how would that be arranged?

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Answer 4

Russ G Author

Level 1

82 points

Mar 28, 2020 6:31 PM in response to Lanny

"Disk Utility" is the software to use but knowing that does not describe the process. Anybody else willing to flesh this out with something more by way of process? The steps and order I need to do things are missing. The instructions are absent.

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