Problem with erase/install

I've followed Apple's initial instructions, cmd-r etc and opened disk utility. Disk images/OS X Base was highlighted with erase greyed. I switched to Internal, highlighted Macintosh HD and erased that. Back on Disk images OS X Base is showing 1.29 GB used and 719.6 MB free. Is this just the OS X; if so do I leave it or erase it?

If I leave it Sierra will presumably remain. If I erase it I can install Snow Leopard from the original CDs. Can I alternatively download a more recent OS X from the Internet? I'm not sure that, given its age Sierra or even its predecessor El Capitan is a good idea?

What specific model year & Mac are you using? What is it you are trying to accomplish?

When you start up holding command+R, you are accessing the Recovery partition (OS X Base) of the drive. When you are booted from it, you can not erase it. This is why, Mac-Forum members usually recommend creating a bootable USB drive.

If this Mac came with Snow Leopard, I would boot from the disc, use Disk Utility to erase and partition the drive, then install Snow Leopard.

Otherwise, if you already downloaded the other operating systems, and they are listed in your Mac App Store Purchased page, then yes, you can download a different Mac OS X/Mac OS/macOS to install on the drive.

My reply just posted seems to have vanished so here we go again.

My model is a 2010 iMac. It was new in October 2010, specs detailed under my profile.

It seems that I should have started up with Command+Option+R to access the Disk Utility from Apple's servers. As explained earlier I have already erased Macintosh HD from its file ST3500418AS Media, which shows its contents as Macintosh HD (499 GB) after the latter has been erased. This file is listed under 'Internal'.

After restarting and holding down Command+Option+R I clicked on Disk Utility and found OS X Base System highlighted. Is this what I now need to erase?

Another conundrum is the following from:

https://support.apple.com/en-us/HT201314

'You can erase disks or volumes. Erasing a disk deletes all its volumes and files. Erasing a volume deletes all the files on that volume, but does not affect other volumes.'

What is the difference between disks and volumes?

The disk is the entire drive, usually the top most description in Disk Utility sidebar. Since yours I'd a 2010 model, I don't remember what the Disk Name is, but the Base System is a partition on that drive. To erase that partition, you need to select the Disk Drive, not the partition.

ferrarr said:

The disk is the entire drive, usually the top most description in Disk Utility sidebar. Since yours I'd a 2010 model, I don't remember what the Disk Name is, but the Base System is a partition on that drive. To erase that partition, you need to select the Disk Drive, not the partition.

Click to expand...

Thanks for your help. Unfortunately I don't have the options you describe. I have attached an image of what the Disk Utility looks like on my 2010 iMac but, as I was unable to use 'Grab', I had to use the actual image on the 'new' iMac with the wording as it appears on the old iMac.

I have tried erasing ST3500418AS Media but 'erase' failed. Although an attempt to erase Macintosh HD appears to work the drive still appears to be full.

View attachment Disk_utility.pdf

According to that image, your internal HD is NOT erased. In fact, it's 232GB full. Or is that from the NEW mac? It's hard to tell, given what you described. IN any event, the DEVICE (the drive itself) is the ST3500418AS Media level and the mounted volume is Macintosh HD. To fully erase the disk and reinstall the OS, you erase the ST3500418AS, then create a new partition (I'd name it Macintosh HD for consistency) and then select that partition and format it. At that point you have a newly formatted, naked drive. Nothing on it, no OS, no data.

BTW, you cannot erase or format the drive if you are booted from it. To do what I described, you have to boot from something else. It could be a cloned drive, or a USB stick with the OS on it, or just about anything BUT the internal drive.

Perhaps I forgot to mention that the data on my attachment is from my 'new' iMac because I couldn't use 'Grab' to show an image from the old one. The actual data shows the bar all blue with 499.25 GB Used and Zero KB under Purgeable and Free.

I have the original disks for the 2010 iMac. Should I try loading those? I thought the Cmd+Option+r would take me to the online Disk Utility. It looks as if that is not the case.

Alwyn, on the old machine, not the new one, is there a partition indented under the device name like in your screenshot of the old one? Don't bother posting any more pictures of the new system, they aren't really helpful and are just confusing the situation here for me.

BTW, you don't need Grab to do a screenshot. Command-shift-3 will screenshot the entire screen, Cmd-shift-4 will allow you to chose part of the screen. Here is the link from Apple that describes it: https://support.apple.com/en-us/HT201361

Ok, my bad. I forgot to mention, what MacInWin (Jake) mentioned, about the drive you are booting from, being non erasable. No, you do not NEED to erase the Base System, that is the Recovery partition which is what you want to install the Mac OS version from.

Unable to delete this post

MacInWin said:

Alwyn, on the old machine, not the new one, is there a partition indented under the device name like in your screenshot of the old one? Don't bother posting any more pictures of the new system, they aren't really helpful and are just confusing the situation here for me.

BTW, you don't need Grab to do a screenshot. Command-shift-3 will screenshot the entire screen, Cmd-shift-4 will allow you to chose part of the screen. Here is the link from Apple that describes it: https://support.apple.com/en-us/HT201361

Click to expand...

Thanks for the tip re screenshot. I knew it was possible to do that but assumed it wouldn't work unless everything was up and running. I did a restart from the installation DVD but that seems to go to an automatic installation. I took the drastic step of turning off with the power button but the installation DVD hasn't been ejected so I am completely stuck as I have set restart to go to the DVD automatically!

This is all so much more complicated than resetting iPads and iPhones!

Do you have an Apple keyboard, either USB or wireless, you are using? If so, press and hold "eject", top row all the way to the right. Another thing to try, is to hold "esc" down until the disc ejects. One more option is to hold the mouse button.

SUCCESS I think.Thanks Bob and Jake for your patience. I have completed the installation of Snow Leopard but not the Applications Install DVD because, when I clicked Continue the iMac restarted and went straight to the Welcome bit instead of requesting the Applications Install DVD.

I will make clear when I sell it that that bit is still to do unless either of you have further useful suggestions.