Plug compatible

Plug compatible refers to "hardware that is designed to perform exactly like another vendor's product." The term PCM was originally applied to manufacturers who made replacements for IBM peripherals. Later this term was used to refer to IBM-compatible computers. Before the rise of the PCM peripheral industry, computing systems were either configured with peripherals designed and built by the CPU vendor, or designed to use vendor-selected rebadged devices. The first example of plug compatible IBM subsystems were tape drives and controls offered by Telex beginning 1965. Memorex in 1968 was first to enter the IBM plug-compatible disk followed shortly thereafter by a number of suppliers such as CDC, Itel, and Storage Technology Corporation. This was boosted by the world's largest user of computing equipment in both directions. Ultimately plug-compatible products were offered for most peripherals and system main memory. 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. 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.). The original example of PCM mainframes was the Amdahl 470 mainframe computer which was plug-compatible with the IBM System 360 and 370, costing millions of dollars to develop.