Hi. I wish to install El Capitan on my 2015 iMac. I have made a bootable USB disk as per instructions at How to create a bootable installer for macOS - Apple Support
I start up the iMac holding down the option key.
I select the installer external USB HDD.
I choose to install El Capitan BUT now it wants to install on the external HDD. There is no option to instal on iMac's HDD.
What have I done wrong?
iMac
Hello!
+1 to jdo_apple. You'd need to erase your internal hard disk to use the Mac OS Extended (Journaled) format first, then install OS X El Capitan:
Erase a volume using Disk Utility on Mac - Apple Support.
However, why are you installing OS X El Capitan on an iMac (Late 2015)? Your Mac supports macOS Monterey, which is much newer than OS X El Capitan.
Thanks!
Jack
Hello!
+1 to jdo_apple. You'd need to erase your internal hard disk to use the Mac OS Extended (Journaled) format first, then install OS X El Capitan:
Erase a volume using Disk Utility on Mac - Apple Support.
However, why are you installing OS X El Capitan on an iMac (Late 2015)? Your Mac supports macOS Monterey, which is much newer than OS X El Capitan.
Thanks!
Jack
Hello Michael Vallanc,
Welcome to Apple Support Communities. We see that you've been following How to create a bootable installer for macOS - Apple Support
So we're on the same page, Can you tell us which Mac model, and macOS version are you using?
Another question would be to check what format the internal hard drive is, as only Mac OS Extended would be supported for OS X El Capitan, so if the hard drive is already formatted Apple File System (APFS) that could explain why you are not seeing the internal hard drive as an option to install OS X El Capitan: File system formats available in Disk Utility on Mac - Apple Support
Another good step would be to startup into macOS Recovery Mode and run First Aid on the internal hard drive and see if that shows any issues: How to repair a Mac disk with Disk Utility - Apple Support
We hope this information is useful. Kind regards.
Thank you. Yes, erasing the HDD was necessary, then i could choose install OS X. Success.
The iMac is painfully slow, with spinning beachball on every action. I cannot upgrade RAM on the 2015 model so decided to install its original OS X.
Michael Vallance wrote:
Thank you. Yes, erasing the HDD was necessary, then i could choose install OS X. Success.
The iMac is painfully slow, with spinning beachball on every action. I cannot upgrade RAM on the 2015 model so decided to install its original OS X.
Glad you can now install OS X El Capitan!
However, have you considered using an external SSD as your startup disk? While the hard disk found in your Mac is perfectly suited to light tasks, such as email and web browsing, but for more advanced tasks, and for users who want the maximum performance from their Mac, this hard drive does have its limitations. However, using the external SSD as your startup disk to run macOS and access your data will make your Mac 10 to 40 times faster for storage, and in turn, make your entire Mac much faster and even better. Plus, you could upgrade to macOS Monterey, the latest version of macOS, and have excellent performance.
To learn more, see: Use an external SSD as your startup disk … - Apple Community.
Jack
Installing El Capitan to downgrade macOS
