install Yosemite on a blank hard drive

Not crazy at all.

There are, at least, two methods available to you:

1. Create a bootable installer, or
2. Create a bootable clone << not really available as your iMac would need to be operational to create the clone ... but would be a good idea once it is.

Since you have an older Mac Pro, the first method would be the one you would want to try. You would use the Mac Pro to create the bootable installer onto a USB stick/drive. Then boot up the iMac with it. From there you would go through the process of installing OS X.

This process is relatively straight forward. All it requires is an external USB stick/drive with at least 14GB capacity, and a full installer of the version of OS X that you want to install on your iMac. Since we know that Mac cannot be upgraded past El Capitan, you will want the full installer for that. The following support article should take you through the steps: Create a bootable installer - Apple Support

Note that your Mac Pro must be running El Capitan or later to be able to download the El Capitan installer from Apple.

The A1224 should be a 2007 model. That one can be upgraded up to 10.11.6 (El Capitan) ... so a bit better, and you can still get El Capitan from Apple here: How to download and install macOS - Apple Support

A pre-2009 iMac, that originally came with Snow Leopard or earlier, did not include a Recovery partition on their internal drives. That would mean that the typical method to re-install OS X was to use the provided installation discs with the computer.

Alternately, if you don't have them, you would acquire a OS X Snow Leopard installation disc from Apple, and then, boot up your system with it to get it installed. However, I don't believe Apple still sells them. Hopefully, the support article I provided you a link for may help you around this.

Ref: https://www.macworld.com/article/672001/command-r-not-working-how-to-reinstall-macos-if-recovery-wont-work.html

Ok, a successful creation of the bootable installer should provide you with the PNY that will be bootable and should start the installation process for El Capitan.

... so, after it is created, you would remove it from your Mac Pro, and then, with the power-off insert it into a free USB port on your iMac. You would then power-up the iMac. If it doesn't "see" the bootable installer, you can power-up the iMac again, but this time hold down the alt/option key until the Startup Manager appears. From there, you would select the PNY from where you want your Mac to start from.

Ok, let's backtrack a bit to help me understand where you are with this process. So here's a few questions:

• You're using your Mac Pro to create the bootable installer ... correct?
• Your Mac Pro is running OS X El Capitan or newer operating system ... correct?
• You successfully downloaded a full installer of El Capitan from the Apple site, and that installer shows up in the /Applications folder on your Mac Pro ... correct?
• You ran the Terminal app, and then, entered the following command after the prompt: sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app

In the above command be sure to change "MyVolume" with the actual volume name of the USB drive.

SchenkerBob wrote:

Disk Utility shows my thumb drive with it's product name as "PNY USB 2.0 FD Media." I renamed it "64GB flash 1" so I could tell which one it is, as I have more than one of these.

Ok, "PNY USB 2.0 FD Media" is the name of the physical device. In Disk Utility (if you selected "Show All Devices) it would appear at the same level as your Mac's internal drive. In my case, my Mac's drive is named: APPLE HDD HT..."

Under that physical drive would be the names of any volumes that are on that drive. By default, on a newer formatted drive, it would only have one volume. This is the one you could rename as you see fit. Again, using my Mac's internal drive, that single volume is called: Macintosh HD

So, in this case using the Disk Utility, you should see your PNY external drive under the External category in the left-side window. Below it would be the name of the single volume. That's the volume that you should rename. To make the command simpler, rename that volume to "MyVolume" (without the quotation marks.)

Now, let's look at that command line, in more detail.

sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app

• sudo /Applications/Install| OS| X| El| Capitan.,app/Contents/Resources/createinstallmedia
  • The "|" symbol is used when there is a space in the name. You would find the installer in the /Applications folder, with the name: Install OS X El Capitan.app. Thus those symbols were added to denote that there are spaces.
  • The app that needs to run, createinstallmedia, is located within the app's contents (although you only see a single file, it is comprised of several folders within it.
  • So, this part of the command is telling where the createinstallmedia app is located to run it.
• --volume /Volumes/MyVolume
  • This is a qualifier for the createinstallmedia app to where it will create the installer on the PNY drive. Your Mac "sees" this location in the /Volumes/ folder when you inserted the drive into your Mac.
  • MyVolume is just a placeholder name. The name you created would be used instead. However, since it has spaces, you would need to add the "|" symbols. Again, to make this easier, you can just rename it to MyVolume.
• --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app
  • This is a second qualifier for the createinstallmedia app. It tells the it where to find the installer file. This would be the path to it on your Mac.

I'm sorry if this is becoming too difficult, but it is the only way I know to create an installer ... outside having the original installation discs that came with this Mac.

I will look forward to your results.

Keep in mind the purpose of the bootable installer. The best way to look at its purpose is with an example. Let's say you have a few old Macs that you want to "get running" again where you had to replace their internal drives or their existing drives were completely erased. Kinda like what you have in your case. These are very common so you are in good company. A lot of us like keeping their old Macs and do what we can to keep them going.

You would use this installer to boot up these Macs, and then, use it to re-install an operating system on it.

This method is typically used when an older (pre-2010) Mac:

• Does not have a recovery partition or its missing on their internal drive, or
• Does not have the Internet Recovery Mode option in their firmware, or
• Its original (or replacement) installation discs are no longer available / the Mac's CD drive is not functional

AFAIK, all 2005 iMacs came with G5 PowerPC processors. They also cannot be upgraded past OS X 10.5 (Leopard) ... so creating a OS X Yosemite drive won't help you here.

Per chance, do you still have the original installation discs that this Mac came with? If so, you may be able to boot up with that disc to restore an operating system on it.

A "2008" model will still only get you to El Capitan. You would have to have a Late 2009 model to go beyond that.

... and yes, one issue will be with attempting to access secured websites (think financial institutions) as it wasn't until OS X 10.9 Mavericks that Apple added TLS 1.2 support.