How to update Old iMac to OS X 10.12 Sierra

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How to update Old iMac to OS X 10.12 Sierra

I have a 21.5" mid 2010 iMac with 4 Gig of RAM, Currently it is running OS X 10.10.5 Yosemite. I want to connect my iPad and iPhone to the computer and upgrade them from IOS 12 to 14. However, I have to update my iMac first. I can't seem to get Sierra to work. I have downloaded the installer from: https://support.apple.com/en-us/HT211683

And when I open it up and run it nothing happens. I tried to download it from the App Store and it failed to download.

I could install OS 10.13 High Sierra, however I would have to change the startup drive to a different partitioning scheme and I don't know how to do that on the startup drive and then install.

Any ideas.

Thanks,

Bob

Posted on Jan 1, 2021 3:51 PM

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Answer 1

Best reply

Eau Rouge

Level 8

42,554 points

Jan 1, 2021 4:46 PM in response to Bob Cohen

If you do have an operating system on your mac and it is functioning then you can download

Sierra using this method.

How to get old versions of macOS – Apple Support

Go to Download macOS and click on macOS Sierra 10.12

This downloads InstallOS.dmg to your Downloads folder.

The next section can only be done on a mac that is capable of running Sierra,

a mac that came preinstalled with an OS later than Sierra will refuse to do the next bit.

When downloaded open to get InstallOS.pkg, double-click o

that and an installation window will open, read and follow the prompts,

this does not install Sierra but uses the InstallOS.pkg to create the

Install macOS Sierra.app which you will find in your Applications folder.

(If the installation window asks which disk you want to install to, you must pick

the disk that you are booted to at the time. Not any internal or external disk that

you want to eventually install Sierra on, that is for later.)

To start the installation of Sierra double click on the Install macOS Sierra.app.

The copy of the install app self deletes after installing Sierra, so make sure you keep a copy of the InstallOS.dmg

if you need it in future, or you could just make a copy of the Install OS X Sierra.app prior to installing and moving it to

an external drive for safe keeping.

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Answer 2

Bob Cohen Author

Level 2

341 points

Jan 1, 2021 4:57 PM in response to Bob Cohen

Thanks for helping me find what I was down loading. However, I can’t install it on my startup drive because I get the message “This Disk doesn’t use GUID partitions”. If I go to Disk Utility and try to partition the startup drive, it wants to erase the startup drive. What happens then?

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How to update Old iMac to OS X 10.12 Sierra

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