One of the great things about Macs is that the OS is bootable on any Mac machine, regardless of which computer it was originally installed on. This means that if your desktop breaks, you can grab the drive and boot it from your laptop instead, without having to worry about data recovery services and lost work time.
Another powerful use for this is that you can install OSX onto an external hard drive, and have a completely portable OS. Today I’ll be doing just that with OSX Lion in order to test it out, but this applies just as equally to any previous versions of OSX.
What This Isn’t
This has nothing to do with a Hackintosh or booting OSX on Windows machines. This also isn’t about installing OSX from an external drive (if you can’t read DVD’s for instance). Rather this is about installing a working OSX system on an external drive, so that it’s portable and able to be easily moved around and booted from any machine.
The only limitation is that both machines must use the same architecture. This means you cannot install Lion to a USB drive then boot it on your old Power PC – but you could install it from an Intel i5 based machine and boot from an Intel Core2Duo.
You may be thinking this would useful to run a testbed install of OSX to trial new apps or software, but it’s more designed for the portability aspect of being able to boot the OS anywhere, and to test Lion while still keeping everything on your primary machine as it is. OSX Lion will actually allow you to run two additonal copies of the OS inside a virtual machine for testing purposes.
Read t he entire article here:
How To Install OSX Lion On An External Drive To Test It Out [Mac].