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User profile for user: hookgrip10
hookgrip10 Author
User level: Level 1
8 points

How to install El Capitan on an SSD before installing in old iMac

I'm trying to breathe new life into my late 2009 iMac. The HD finally died and I bought an SSD upgrade kit from iFixit.com. I understand I have to format and partition the SSD before I install it, and I can do that using my MacBook Pro.


My question is, when (and how) do I install OS X El Capitan onto the SSD? All the instructions I've found say to download El Capitan from the App Store, and that it will save the installer to Applications, which can then be installed on the SSD via command line. But the only link I've been able to find for El Capitan just saves a DMG file to my Downloads Folder.


I'm not sure what to do with that, or how to get it from the DMG in Downloads into an App in the Applications folder. Obviously I don't want to install El Capitan on my new MacBook Pro, I just want to use my MacBook to set up the SSD with El Capitan before I install it into the 2009 iMac.


If I double-click on the El Capitan DMG file, will it ask me where I want to install El Capitan (and will I be able to select the newly formatted SSD?) or will it automatically try to install it on my MacBook?

iMac, macOS 10.12

Posted on Oct 27, 2020 6:44 PM

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User profile for user: Eau Rouge
Eau Rouge
User level: Level 8
42,596 points

Posted on Oct 28, 2020 1:19 AM

What you need to do its download the InstallMacOSX.dmg and process that to get the Install OS El Capitan.app

which you use to create a bootable USB installer that you then use to install El Capitan on your new SSD.


Read these instructions.


Click on the link below.


How to upgrade to OS X El Capitan – Apple Support


Go to Section 4 and click on Download OS X El Capitan.


This downloads InstallMacOSX.dmg to your Downloads folder.


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

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


When downloaded open to InstallMacOSX.pkg, double-click on

that and an installation window will open, this does not install El Capitan

but converts the InstallMacOSX.pkg to the Install OS X El Capitan.app which 

you will find in your Applications folder, it should be 6.2GBs in size.


 (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 El Capitan on, that is for later.)


Create a bootable USB installer disk using the Install OS X El Capitan.app

in the Applications folder and the createinstallmedia command in the Terminal app. 


Read the instructions here,

How to create a bootable installer for macOS – Apple Support


Having made the bootable USB installer you are ready to install to your new SSD

which you have inserted into your iMac.


Plug the bootable USB directly into the iMac.

Restart the mac while pressing and holding down the option/ alt key.

In a couple of minutes you will see the Startup Manager, select the USB

and press Return.


When booted to the USB you will see a Utilities panel, select Disk Utility and press Continue.


In the left hand panel highlight the Disk not the indented Volume, click Erase.


Give the Disk a name.

Format: Mac OS Extended (Journaled)

Scheme: GUID Partition Map

Click Erase.

When Done Quit Disk Utility.


Click on Install OS X press Continue the installation process should start up

follow the prompts.

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Question marked as Top-ranking reply
User profile for user: Eau Rouge
Eau Rouge
User level: Level 8
42,596 points

Oct 28, 2020 1:19 AM in response to hookgrip10

What you need to do its download the InstallMacOSX.dmg and process that to get the Install OS El Capitan.app

which you use to create a bootable USB installer that you then use to install El Capitan on your new SSD.


Read these instructions.


Click on the link below.


How to upgrade to OS X El Capitan – Apple Support


Go to Section 4 and click on Download OS X El Capitan.


This downloads InstallMacOSX.dmg to your Downloads folder.


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

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


When downloaded open to InstallMacOSX.pkg, double-click on

that and an installation window will open, this does not install El Capitan

but converts the InstallMacOSX.pkg to the Install OS X El Capitan.app which 

you will find in your Applications folder, it should be 6.2GBs in size.


 (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 El Capitan on, that is for later.)


Create a bootable USB installer disk using the Install OS X El Capitan.app

in the Applications folder and the createinstallmedia command in the Terminal app. 


Read the instructions here,

How to create a bootable installer for macOS – Apple Support


Having made the bootable USB installer you are ready to install to your new SSD

which you have inserted into your iMac.


Plug the bootable USB directly into the iMac.

Restart the mac while pressing and holding down the option/ alt key.

In a couple of minutes you will see the Startup Manager, select the USB

and press Return.


When booted to the USB you will see a Utilities panel, select Disk Utility and press Continue.


In the left hand panel highlight the Disk not the indented Volume, click Erase.


Give the Disk a name.

Format: Mac OS Extended (Journaled)

Scheme: GUID Partition Map

Click Erase.

When Done Quit Disk Utility.


Click on Install OS X press Continue the installation process should start up

follow the prompts.

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How to install El Capitan on an SSD before installing in old iMac

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