Problems partitioning my hard disk

[momech]

Hi all! Trying to partition my hard disk here but running into problems...

I'm running Yosemite 10.10.5 on a 27-inch, late 2013 iMac, 1TB of disk

I've decided to make a small partition on my disk and am trying to install Catalina on that. My Mac can run up to Catalina 10.15.7

But I'm running into problem after problem!

I created the partition, that went fine, its just over 80GB in size.

My plan, following this YouTube tutorial:

https://www.youtube.com/watch?v=C3R2xTPLhgc

was to create the partition, download the Catalina OS, then choose Hard Disk 2 as destination and install it there.

I quickly found out that Catalina was never released as a .dmg file so that plan fell through.

Instead I downloaded El Capitan from the Internet Archive and thought I'd try doing my plan in stages.

But when I try to install El Capitan on HD2 I'm told "OSX can't be installed on this disk. OSX isn't installed"

I don't get it? What did I miss?

How can I have created a partition with no OSX? What do I need to do next?

Very grateful for any tips!

 

[Fishrrman]

Don't try to do what you're trying to do.

If you want to experiment with Catalina, do this:
Buy a small, 2.5" SATA SSD. 256gb should do. About $24.
Something like this:

https://www.amazon.com/Crucial-BX500-240GB-2-5-Inch-Internal/dp/B07G3YNLJB/ref=sr_1_3?crid=2XAZ14M7ESKX8&dib=eyJ2IjoiMSJ9.rEno421c6fKN8lHOneJQtfXcsaVWoMznDRkZ80TulgeQVDqTIdvya8QKJpxsRomtO7Ld-LjWRhjTmWr5FuoAW_e1DS9NW_1YlUUAHsy8ZpeZzxWlE6Mo9hbREzC3drlC7YnTFZtvSdNjcj3Kf6YNaVAm_GD5ItJnxb1pSn_T7mmQwURmSfFtc8C4KqRStfaQZapoS1G7w7Ii4hyRjnrZyesXFW7nXMw6-q-uE9aC1hY.4JPXmOp5AT7nUPv5ODYkh5jTM6IWqyhmzb4xGGBhBRA&dib_tag=se&keywords=2.5%22%2Bsata%2Bssd%2B256gb&qid=1753191560&sprefix=2.5%2Bsata%2Bssd%2B256gb%2Caps%2C76&sr=8-3&th=1

Then, get a USB3.1 gen2 enclosure like this:

https://www.amazon.com/POSUGEAR-External-Enclosure-Tool-Free-Compatible/dp/B0C9TGY9XG/ref=sr_1_1_sspa?crid=2W3HY8ABXQ3W&dib=eyJ2IjoiMSJ9.RW35ur769XE0WVAsFWH904LgnIjaiZDexis0G6KhdOyv4utNuE9qmbD_8PcGLp-dqh-AfGyRoE_DdCxP888q09NQ6kbt_0NPIsQIIqgDTYWZknq25baTEKzTH0UMFRVfdHF-pHXWa4Gz4_zRxRkT9P52bFz-KeOOq0uL7CGuRqlh30LANMzFnsw2KPHrdPnNxBX2qFHmWYNUgsf0mQA25Sr9AaQmneZ7FIXGgHgEpZQ.az1mtnD6JTWrcE7jaY3gY6d0VXiZdzFC_88uZ9S4qLk&dib_tag=se&keywords=usb3.1%2Bgen2%2B2.5%22%2Bsata%2Benclosure&qid=1753191628&sprefix=usb3.1%2Bgen2%2B2.5%2Bsata%2Benclosure%2Caps%2C44&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1

Put the drive into the enclosure, initialize with disk utility.

Now, install Catalina onto this EXTERNAL boot SSD.

If you take my advice, I predict that things will go much better for you...

 

[!!!]

Instead I downloaded El Capitan from the Internet Archive and thought I'd try doing my plan in stages.

I would recommend you download it from this apple.com support article which links to a bunch of macOS installers.

But when I try to install El Capitan on HD2 I'm told "OSX can't be installed on this disk. OSX isn't installed"

This is because, despite the naming, what you're installing is not OS X/macOS, but rather the OS X/macOS Installer, app which you launch which will then guide you through the OS installation process. This is an unfortunate side-effect of how Apple packaged these installers. You need to first install the installer onto a disk that runs macOS. You can also use a tool like pacifist to manually extract the installer, but this is tedious because the installer is not simple.

 

[momech]

Don't try to do what you're trying to do.

If you want to experiment with Catalina, do this:
Buy a small, 2.5" SATA SSD. 256gb should do. About $24.
Something like this:

https://www.amazon.com/Crucial-BX500-240GB-2-5-Inch-Internal/dp/B07G3YNLJB/ref=sr_1_3?crid=2XAZ14M7ESKX8&dib=eyJ2IjoiMSJ9.rEno421c6fKN8lHOneJQtfXcsaVWoMznDRkZ80TulgeQVDqTIdvya8QKJpxsRomtO7Ld-LjWRhjTmWr5FuoAW_e1DS9NW_1YlUUAHsy8ZpeZzxWlE6Mo9hbREzC3drlC7YnTFZtvSdNjcj3Kf6YNaVAm_GD5ItJnxb1pSn_T7mmQwURmSfFtc8C4KqRStfaQZapoS1G7w7Ii4hyRjnrZyesXFW7nXMw6-q-uE9aC1hY.4JPXmOp5AT7nUPv5ODYkh5jTM6IWqyhmzb4xGGBhBRA&dib_tag=se&keywords=2.5%22%2Bsata%2Bssd%2B256gb&qid=1753191560&sprefix=2.5%2Bsata%2Bssd%2B256gb%2Caps%2C76&sr=8-3&th=1

Then, get a USB3.1 gen2 enclosure like this:

https://www.amazon.com/POSUGEAR-External-Enclosure-Tool-Free-Compatible/dp/B0C9TGY9XG/ref=sr_1_1_sspa?crid=2W3HY8ABXQ3W&dib=eyJ2IjoiMSJ9.RW35ur769XE0WVAsFWH904LgnIjaiZDexis0G6KhdOyv4utNuE9qmbD_8PcGLp-dqh-AfGyRoE_DdCxP888q09NQ6kbt_0NPIsQIIqgDTYWZknq25baTEKzTH0UMFRVfdHF-pHXWa4Gz4_zRxRkT9P52bFz-KeOOq0uL7CGuRqlh30LANMzFnsw2KPHrdPnNxBX2qFHmWYNUgsf0mQA25Sr9AaQmneZ7FIXGgHgEpZQ.az1mtnD6JTWrcE7jaY3gY6d0VXiZdzFC_88uZ9S4qLk&dib_tag=se&keywords=usb3.1%2Bgen2%2B2.5%22%2Bsata%2Benclosure&qid=1753191628&sprefix=usb3.1%2Bgen2%2B2.5%2Bsata%2Benclosure%2Caps%2C44&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1

Put the drive into the enclosure, initialize with disk utility.

Now, install Catalina onto this EXTERNAL boot SSD.

If you take my advice, I predict that things will go much better for you...

Thank you! I like that idea
I've been advised to make a bootable USB... is this basically the same thing, but with an SSD instead of a USB?

If I do this can I boot to this disk to use Catalina and surf the web?