Install ML to external HD?

[Greymarch]

I have a non-retina 2012 15in MacBook Pro with a SSD I installed myself, running Lion 10.7.4. I use my laptop at work, and my work has informed me to not upgrade to ML because it is unlikely my computer would still be compatible with work.

I have an external hard-drive I use as a backup for my MacBook Pro. I used carbon copy to make a backup of my MacBook Pro to the external HD. I can boot from the external HD. The external HD has Lion on it, and I can use the external HD as my operating system if I have the need. My question is, can I install ML onto the external HD and use the external HD to test ML, without affecting my MacBook Pro and the SSD currently residing in the MacBook Pro? How would I install ML onto my external HD without affecting the Lion install that already exists on the SSD inside the MacBook Pro? If installing ML onto the external HD would in any way change my MacBook Pro when I boot from the SSD inside the laptop, then I cannot install ML onto the external HD.

 

[SimonTheSoundMa]

Yes you can. When you run the installer, just choose another drive, very similar to using the Apple installer for apps.

I'd create a new partition on the external drive using Disk Utility first. 20GB should be enough. Then install to that partition. Once your happy testing ML, just delete the partition and resize the other back again.

 

[53kyle]

Just choose your external hd from the mountain lion installer and wait for it to install.

EDIT: when I was typing this post, I forgot to reload the page to see if anyone else had replyed yet.

 

[SimonTheSoundMa]

I tried it with an external drive. When it comes to reboot sometimes OS X will reboot back to the internal drive. Just keep your finger on the option button before the gong at boot and choose the external drive. The installer will then complete.

You wont ruin anything if it does boot to the internal drive. Just reboot again and choose the drive.