Program compatible
From Computer History Wiki
Program compatible is a term applied to either a new hardware system (such as a CPU or device controller) or software system (e.g. an operating system) which is so functionally identical to an earlier one that programs written for the earlier one will run with the new one with no changes.
It usually means that the original object code can be used as-is, but sometimes re-compilation, or some similar step, will be needed.
One early, famous, example was the IBM System/360 line, in which it was a deliberate design goal that almost all the various CPU models were program compatible, so that a customer whose processing needs had grown could trivially upgrade to a more powerful model.
