Plug compatibility is a characteristic of computer hardware that performs exactly like that of another vendor.["Making the move into IBM-compatible peripheral products was a natural adjunct to products being developed for OEMs." ] Later plug-compatible mainframe (also PCM) referred to IBM-compatible mainframe computers.["plug-compatible mainframe (PCM)." ] PCM can also mean plug-compatible machine or plug-compatible module.
Plug compatibility and peripherals
Before the rise of the plug-compatible 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 examples of plug-compatible IBM subsystems were tape drives and controls offered by Telex beginning 1965.["Expected to produce $1 billion in revenues during fiscal 1980, CDC's peripherals business, advancing at 33% annually, is the fastest growing revenue producer within the company's diverse product line." ] Itel, and Storage Technology Corporation. This was boosted by the world's largest user of computing equipment, the US General Services Administration, buying plug-compatible equipment.["GSA has initiated a Government-wide program to replace existing leased peripheral devices with lower cost plug-to-plug compatible equipment offered by independent suppliers. This program was aimed at permitting competitive offers of peripherals by independent suppliers." ]["... to allow the use of IBM plug-compatible peripherals on the CDC 6400, 6600 and 7600 systems installed at the LBL Computer Center. This has given the ability to replace unreliable CDC tape drives and controllers and overpriced CDC disk drives and controllers with their IBM plug-compatible counterparts." ]
Eventually there were third-party plug-compatible alternatives to most first-party peripherals and first-party system main memory.
Plug compatibility and computer systems
A plug-compatible machine is one that is 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
Plug compatibility and IBM mainframes
The original example of plug-compatible mainframes was the Amdahl 470 mainframe computer which was plug-compatible with the IBM System 360 and 370, costing millions of dollars to develop. Similar systems were available from Comparex,
Fujitsu,
["LEAD: Beating I.B.M. to the punch by one day, Fujitsu Ltd. announced a series of computers today that ..." ] and Hitachi. Not all were large systems.
["A 3200 system can include up to 16M bytes, with virtual memory freeing programmers from artificial memory constraints. It can handle all major programming languages, such as Cobol, Fortran, PL/I, APL, Basic, and Assembler. The National CSS 3200 series will range in price from $200,00 to $600,000." ][Trilogy Systems Corporation was started by Gene Amdahl together with his son Carl Amdahl and Clifford Madden.] Most of these system vendors eventually left the PCM market.
["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." ]["A notable PCM failure was Storage Technology (StorageTek), which was for many years one of the more successful of the plug-compatible peripheral suppliers. StorageTek's attempt to make its own processor and become another Amdahl or HDS almost drove it out of business. It took years to recover ..." ]["Amdahl ...pulling out of the plug-compatible market in 2000 following IBM's launch of 64-bit systems." ] In late 1981, there were eight PCM companies, and collectively they had 36 IBM-compatible models.
Non-computer usage of plug compatibility
Plug compatibility may also be used to describe replacement criteria for other components
["A universal four-contact plug and jack assembly ..." ] 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 standards 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. However, nothing prevents a company from developing follow-on products that are backward-compatible with its own early products.
See also
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Bug compatibility
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Clone (computing)
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Computer compatibility
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Drop-in replacement
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Hercules (emulator)
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Pin compatibility
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Proprietary hardware
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Second source
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Vendor lock-in
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Honeywell 200, chasing the IBM 1401 market
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Xerox 530, chasing the IBM 1130 market
