Thanks for those two similar helpful replies.
I have never used Time Machine, as the early versions seemed to be just a pain.
I guess things have now improved, and I will try it - after finding out more about it.
A pal has used TM on a MBP but after a crash by iPhoto '11, found that the most recent work had not been saved by Time Machine.
I don't have details of time interval specified.
As far as I can see, with a laptop such as MBP, used anywhere in the house, TM can only work when you have connected a large bulky external hard drive to it. So you have to remember to make that connection every so often, otherwise the "automatic" back up will not be taking place.
For " use a memory stick" I guess that means something like this:
Please tell me if I am wrong.
Thanks for the info.