What (who) is expansion slots - definition
![S-100]] backplane which housed both the [[Intel 8080]] [[mainboard]] and many expansion boards](https://commons.wikimedia.org/wiki/Special:FilePath/Altair 8800b Computer.jpg?width=200 "S-100]] backplane which housed both the [[Intel 8080]] [[mainboard]] and many expansion boards")
![ISA]] expansion cards from the 1980s](https://commons.wikimedia.org/wiki/Special:FilePath/DIP switch 01 Pengo.jpg?width=200 "ISA]] expansion cards from the 1980s")
![Rack of [[IBM Standard Modular System]] expansion cards in an [[IBM 1401]] computer using a 16-pin gold plated edge connector first introduced in 1959](https://commons.wikimedia.org/wiki/Special:FilePath/IBM 1401 card cage.jpg?width=200 "Rack of [[IBM Standard Modular System]] expansion cards in an [[IBM 1401]] computer using a 16-pin gold plated edge connector first introduced in 1959")
![[[Thunderbolt 3]] connector introduced by [[Intel]] in December 2015 multiplexes up to 4-lanes of [[PCIe 3.0]] and 8-lanes of [[DisplayPort]] 1.2 and can support an external [[docking station]] housing one or more expansion cards with enough bandwidth to drive a mid-range [[GPU]]](https://commons.wikimedia.org/wiki/Special:FilePath/Thunderbolt 3 Cable connected to OWC Thunderbolt 3 Dock.jpg?width=200 "[[Thunderbolt 3]] connector introduced by [[Intel]] in December 2015 multiplexes up to 4-lanes of [[PCIe 3.0]] and 8-lanes of [[DisplayPort]] 1.2 and can support an external [[docking station]] housing one or more expansion cards with enough bandwidth to drive a mid-range [[GPU]]")
Wikipedia
In computing, an expansion card (also called an expansion board, adapter card, peripheral card or accessory card) is a printed circuit board that can be inserted into an electrical connector, or expansion slot (also referred to as a bus slot) on a computer's motherboard (see also backplane) to add functionality to a computer system. Sometimes the design of the computer's case and motherboard involves placing most (or all) of these slots onto a separate, removable card. Typically such cards are referred to as a riser card in part because they project upward from the board and allow expansion cards to be placed above and parallel to the motherboard.
Expansion cards allow the capabilities and interfaces of a computer system to be extended or supplemented in a way appropriate to the tasks it will perform. For example, a high-speed multi-channel data acquisition system would be of no use in a personal computer used for bookkeeping, but might be a key part of a system used for industrial process control. Expansion cards can often be installed or removed in the field, allowing a degree of user customization for particular purposes. Some expansion cards take the form of "daughterboards" that plug into connectors on a supporting system board.
In personal computing, notable expansion buses and expansion card standards include the S-100 bus from 1974 associated with the CP/M operating system, the 50-pin expansion slots of the original Apple II computer from 1977 (unique to Apple), IBM's Industry Standard Architecture (ISA) introduced with the IBM PC in 1981, Acorn's tube expansion bus on the BBC Micro also from 1981, IBM's patented and proprietary Micro Channel architecture (MCA) from 1987 that never won favour in the clone market, the vastly improved Peripheral Component Interconnect (PCI) that displaced ISA in 1992, and PCI Express from 2003 which abstracts the interconnect into high-speed communication "lanes" and relegates all other functions into software protocol.
