Eugene's observations

When your computer becomes slow or your disk drive fills up or you upgrade to a new computer because of failure, you may want to copy things to the new faster disk drive.  Clearly the copying of documents, photos, and music is relatively straight forward but there are other things to be copied: saved email and the matching accounts, favourite bookmarks from your browsers, address books, and sometimes programs.  It?s not that straightforward.

With the plain data files such as documents and spreadsheets you need to be sure that the access control data that accompanies them matches the account(s) of the destination.  Music may need to be de-authorised then authorised and catalogued. 

Usually programs cannot be copied (unless designed as portable) as they rely on registry entries and dynamic link library registration and maybe also a programming framework.  There is an exception though: where nothing except the disk drive is changing it is often possible to migrate programs by duplicating the disk signature.

The way that all the main software suppliers prevent loss of income by people sharing their programs and only paying once is to cause them to check for a duplicate product key or activation code.  But how do they know when a product is legitimately reinstalled on the same computer ?  The answer is that they record details of the computer that cannot easily be replicated; so if the MAC address of a network card is different or the serial number of the motherboard has changed they will know that an attempt at piracy is afoot.

But when nothing other than a disk drive is being changed it is possible to duplicate the disk signature to allow the programs now residing on a different device to work as before without the need to buy a new license.  Not doing so may seem cheaper in the short term, but when the cost of additional licenses is factored in it turns out cheaper to have a copy operation professionally done.

However if simply adding a new disk drive to an existing one the opposite is true: disk signatures must be confirmed to differ as if a collision occurs Windows will become unbootable.