I had an uncle who was involved in the initial rollout of ATMs in the United Kingdom, for one of the major banks here --- Barclays, maybe? He was managerial tra

I had an uncle who was involved in the initial rollout of ATMs in the United Kingdom, for one of the major banks here --- Barclays, maybe? He was managerial track rather than engineering, but he'd still tell horror stories about the high-level executive discussions about the fundamental technology. Seems there were two choices: the one where PINs were held centrally and all ATMs had to be connected to a phone line so they could validate them; or the one where PINs and your balance were stored on the card, which allowed ATMs to be completely disconnected and so be much more flexible (and cheaper). Luckily they chose the right one. Also I have heard, but cannot find a reference for right now, that due to a bug they managed to issue a large proportion of the early cards all using the same PIN. This was apparently the best kept secret in banking until they managed to get them all changed. If anyone's heard of this, I'd love to know more about what happened.