Quantum computing has been attracting considerable attention over the past few years. Some believe it will revolutionise computing. Others question how long it will take before the technology delivers meaningful commercial benefits. And, as with almost every major technological development, there are already predictions about which existing technologies it will replace. Including the mainframe. But will quantum computers actually replace systems such as IBM Z? And perhaps more importantly, what does quantum computing mean for organisations that rely on mainframes to process and protect some of their most important information? I believe there are two very different aspects worth considering. [...]