IBM Z

IBM Z is the name of IBM's mainframe hardware line. Earlier generations were called System/360, System/370, System/390 and zSeries; the "z" stands for zero downtime, which tells you what the design optimises for.

A single machine is physically about the size of a couple of large fridges, and is usually installed in pairs or more across separate sites so that work can survive losing a whole data centre. Inside, it carries its own processors, memory and dedicated input/output hardware that moves data to and from storage without interrupting the main processors.

You will rarely interact with the hardware directly. Most people who work on the mainframe spend their day inside an operating system running on it, connecting over the network from an ordinary computer.

The name matters mainly because it is how the industry labels itself. Job titles, certifications, conferences and product documentation all say "IBM Z" or "Z", and knowing that the term refers to the hardware family saves a lot of confusion early on.