Double disk

Hello,

Your screenshots show the volumes (partitions) existing on the physical hard drive.

I'm not sure in detail how you proceeded, but what needs to be done is to make the physical disk visible, that is to say, the hardware part. To do this, go to Disk Utility and select the View menu / Show All Devices, to see the exact contents of the physical disk. We can already see that there are partitions in Mac OS Extended format and APFS format.

For Catalina, the APFS format should be used. This APFS format is the standard format starting from Mojave (the version just before Catalina). Previously, the format to choose was Mac OS Extended (Journaled).

At this stage, what I would do is boot from the recovery partition, meaning start the Mac while holding down these two keys

cmd R

Then
- launch Disk Utility and completely erase the disk, choosing Mac OS Extended (Journaled), then
- exit Disk Utility
- request to reinstall Mac OS

This will be done via the internet from Apple servers, so a good internet connection is required, preferably wired.

Then, depending on the installed version, you'll need to update or not, and reuse Boot Camp for Windows if necessary.

https://support.apple.com/fr-fr/HT204904

https://support.apple.com/fr-fr/guide/mac-help/mchlp1599/10.13/mac/10.13

Best regards

--
iMac G5 - iMac mid-2011 - Macbook Air M1

Good evening and thank you for this information
When I am in Disk Utility, which disk should I erase?
When I expand the presentation, I see Apple HDD ST 1000dm003 Media
Below contains disk1
Then Macintosh H
Then Macintosh HD - Data
Then Macintosh HD - Data
And finally Untitled

Thank you

The line "HDD ST 1000dm003 Media" should be the physical part; normally, this is the line you would need to select to erase the disk. I'm not sure if this will be accepted, as the recovery partition is included there. Normally, this recovery partition should be visible on a line named "OS X base"... that you don't see??

Could you please attach a screenshot showing everything after selecting the line: "HDD ST 1000dm003 Media"?

--
iMac G5 - iMac mid-2011 - Macbook Air M1

Here is the screenshot


Just in case, if I delete the two volumes Macintosh HD-Data by clicking on - at the top left in volumes, will I be able to reinstall mac?

I made a Catalina USB stick with DiskMaker X9 and the Catalina download I obtained from the store
Is this a solution?

Thanks

What I would do in this situation is select the physical disk, as shown in this last screenshot, then click on "Erase," which doesn't seem grayed out.

If that's denied, you need to select the line Container disk1, and click on Erase...

Then, select the physical part again, then partition, and delete the "Untitled" partition.

The goal is to remove all these volumes in favor of a single volume before reinstalling the system.

However, if you can boot from the USB key (hold the alt key while starting up), that's even better; from Disk Utility, you completely erase the physical HDD ST 1000dm003 Media to then install Catalina. You'll then have a perfectly clean internal disk with a single volume.

--
iMac G5 - iMac mid-2011 - Macbook Air M1

Hello
I think it's good:


So I deleted the volumes, then I changed the boot disk to boot from my USB drive and I reinstalled. USB prepared with this method: https://www.youtube.com/watch?v=Aj4JkA4EN-o
However, I named my disk incorrectly, little rush...
If I have to reinstall Catalina, should I go through the USB drive?
And last question, I've heard about external SSDs. If I understand correctly, you can install your OS on it and use it like a hard drive.
According to my readings, on my iMac from late 2013, it's not possible to install Big Sur.
Is this due to hardware limitations since I have a 1TB HDD and 8GB of RAM?
Thank you

Hello,

- To create a bootable USB drive, it's better to follow Apple's instructions rather than going through YouTube; it's often more reliable:
https://support.apple.com/fr-fr/HT201372#create

- An iMac from late 2013 can support up to Catalina. So, no Big Sur is possible.

- It's always possible to rename an external drive at any time.

- To reinstall Catalina, yes, going through the USB key is preferable if it's already ready, as it saves time since you won't rely on an internet connection, and because it will be possible to completely erase the internal drive by doing a full format of the physical part before installation – so a completely new system, including the recovery partition.

- Using an external SSD as a startup disk is possible, but not really interesting since the connection between the Mac and the SSD will be through a USB port specific to the Mac, which has limited speed. I tested this option on my mid-2011 iMac, but ultimately it was even slower to boot than from a regular external drive. However, an external SSD for storage is definitely a good idea.

--
iMac G5 - mid-2011 iMac - MacBook Air M1

Good evening and thank you
late response, not always on site
thank you