Mac computer with non mac keyboard. Use button Alt in place of Option key select boot hard drive
If you own a mac.
And you'd like to boot into the hard drive select screen... just press the "Option" button.
But if you have a non-mac keyboard.. in my case I had a pc dell keyboard.
The alternative is just the "Alt" key.
In this video I boot into the hard drive partition select screen on my old imac from 2011.