Why 64-bit? It seems that is a question with many answers! For some, it will be the need to address more than 2GB or 4GB of memory, for others the need for wider registers and greater accuracy of 64-bit data processing, for still others the attraction of a larger register set. Either way, the 64-bit train is gathering speed and if you don't get on board it may leave you behind!
Whatever your reason for looking to move to 64-bit, it is likely that you will have a body of legacy software which will need porting as well as new code which needs writing. This paper is designed to help with both processes.
We'll start with a quick look at the evolution of the ARM architecture which has brought 64-bit to reality.