It's amazing how reliable modern computers are, considering the power and capacity they have for very complex applications. It has lulled us all into idea that nothing goes wrong anymore... The software is evolving all the time (and getting bigger!) but the hardware can go catastrophically wrong very quickly and you have to accept it will do it at the worst possible moment - now when did I back up last! Not surprisingly my Macs are now obsolete - the older one is marooned at OS Mavericks, and I can't update the OS on my main iMac any higher than its current state El Capitan, or add any more RAM which is probably more important. However I am now semi retired so only occasionally have to use the system to earn some money... and as if on cue, I upgraded my Adobe Lightroom last night to the major update 'Lightroom Classic CC' - and no, it is NOT working, grrrrr!!!