Plug compatible: Difference between revisions

==PCM and Computer systems==
A '''plug-compatible''' machine is one that has been designed to be [[backward compatible]] with a prior machine. In particular, a new [[computer system]] that is plug-compatible has not only the same connectors and protocol interfaces to peripherals, but also [[binary code compatibility]]—it runs the same software as the old system. A '''plug compatible manufacturer''' or '''PCM''' is a company that makes such products.
 
The term may also be used to define replacement criteria for other components available from multiple sources. For example, a plug-compatible cooling fan may need to have not only the same physical size and shape, but also similar capability, run from the same voltage, use similar power, attach with a standard electrical connector, and have similar mounting arrangements. Some non-conforming units may be re-packaged or modified to meet plug-compatible requirements, as where an adapter plate is provided for mounting, or a different tool and instructions are supplied for installation, and these modifications would be reflected in the [[bill of materials]] for such components. Similar issues arise for computer system interfaces when competitors wish to offer an easy upgrade path.
 
In general, plug-compatible systems are designed where industry or [[de facto standard]]s have rigorously defined the environment, and there is a large installed population of machines that can benefit from third-party enhancements. ''Plug compatible'' does not mean identical replacement. However, nothing prevents a company from developing follow-on products that are backwards compatible with its own early products.
 
One recurring theme in plug-compatible systems is the ability to be [[bug compatible]] as well. That is, if the forerunner system had software or interface problems, then the successor must have (or simulate) the same problems. Otherwise, the new system may generate unpredictable results, defeating the full compatibility objective. Thus, it is important for customers to understand the difference between a "bug" and a "feature", where the latter is defined as an intentional modification to the previous system (e.g. higher speed, lighter weight, smaller package, better operator controls, etc.).
Most of these system vendors evenutally left the PCM market.<ref>"Hitachi has been in the mainframe business for 50 years and currently its AP series of systems are sold to major organisations across Japan. Hitachi Data Systems used to sell Hitachi-made IBM plug-compatible mainframes outside Japan but stopped doing so in 2000." {{cite newspaper |newspaper=The Register |date=May 24, 2017
|title=Hitachi exits mainframe hardware business |url=https://www.theregister.co.uk/2017/05/24/hitachi_exits_mainframe_hardware}}</ref>
 
 
==Non-computer usage of the term==
The term may also be used to define replacement criteria for other components available from multiple sources. For example, a plug-compatible cooling fan may need to have not only the same physical size and shape, but also similar capability, run from the same voltage, use similar power, attach with a standard electrical connector, and have similar mounting arrangements. Some non-conforming units may be re-packaged or modified to meet plug-compatible requirements, as where an adapter plate is provided for mounting, or a different tool and instructions are supplied for installation, and these modifications would be reflected in the [[bill of materials]] for such components. Similar issues arise for computer system interfaces when competitors wish to offer an easy upgrade path.
 
In general, plug-compatible systems are designed where industry or [[de facto standard]]s have rigorously defined the environment, and there is a large installed population of machines that can benefit from third-party enhancements. ''Plug compatible'' does not mean identical replacement. However, nothing prevents a company from developing follow-on products that are backwards compatible with its own early products.
 
== See also ==