Longest Lived Computer Architecture

The longest-lived computer architecture is that developed for the IBM System/360 mainframe computer (usually called System/360 Architecture), which launched on 7 April 1964. This computer's basic architecture – a term which encompasses things like how its memory is organized and addressed, how programs are controlled, and the instruction set used by the processor – is used in a line of IBM mainframes that are still sold and operated today. This means that code written for a System/360 more than 55 years ago should, in theory, run natively on a brand-new IBM Z mainframe.

The most commonly-used computer architectures today are Intel x86 (introduced 1978; used in almost all desktop and laptop computers) and ARM (introduced 1985; used in smartphones and tablets). These have changed more over the years than the System/360 architecture, however.

The reason for the stability of the System/360 architecture is the nature of the mainframe computer market. IBM's customers are typically large businesses (banks, insurance companies, etc.) or government institutions. These groups need to be able to keep software running, without any downtime, for years or even decades. As a result, it is vital that any new hardware they purchase be able to run their "legacy" systems without compatibility issues.