The images from your memory card are transferred onto your hard disk. You would think that would be enough wouldn’t you? But no, as I have told you, your hard disk will fail. Also the images still on the memory card need to be deleted ready for further image taking.
So, copy your files into another area. Perhaps a DVD or an external hard disk. Copying onto a DVD will reduce the chances of them being stolen (external hard disks are nice to steal but who wants a homemade DVD?) but who knows if the media will fail over the years or perhaps there will be a mishap? You can also copy to CDs but the capacity of CDs is far less then that of a DVD.
So, some people copy onto two DVDs or CDs. One is kept separate from the other and is only used for checking that the images have written successfully. This is the master backup. If media changes, you should be able to remake DVDs (or their future counterparts) by recopying either directly or from your computer once more.
External hard drives are cheap and large capacity (mine is 320 GB). They perform very well and are very quick in use. Also, if they are used for backup only, the chances of breakdown are minimised. But – don’t store it near to your computer – they will both be stolen.