I have a mid-2007 24" iMac that I got from someone who didn't have the installation disc. I upgraded the cpu and wifi and RAM awhile back to get the system to run High Sierra, which it does, but not well. I was not impressed with the performance (I still had an old HD in it and not willing to spend on an SSD for an old machine). I want to go back to Tiger and upgrade to a reasonable OSX version that will still perform okay, but I'm stuck since I don't have the installation disc. I've read mixed things. 1. Without the disc, is there any version of OS X retail that will install on this machine? I have an installation disc that is apparently not the right one for this machine, and trying to install just gives a 'can't install on this machine' error when trying to install. 2. I called Apple and they wouldn't sell me the original disc. They said to take it in to a repair place which there's no way I'm going to do. Any other easy way to get an original disc? I haven't seen any on ebay that I'm sure are the right ones... 3. I've read that if you remove the hard drive, hook it up to another mac as an external, install OSX on the external and then install it back in the original machine, it should work. This is a lot of work and I don't want to try it if I'm not going to be successful. Anyone recommend this path?