Thank's guys. But I wasn't suggesting taking a HD out of one PC and putting into another - I was thinking about having a external HD connected to a PC that would be a clone of the drive on the PC. I do this with both my iMac and my wife's Macbook. A couple of years back when I was having 'kernel panics' (bad 3rd party memory chip) on my iMac it was great to be able to boot from a clone - giving me access to all my 'tools'. The stuff on the recovery partition of my HD has some tools, but not all of the ones that I use.