Editing Expansion card (section)

==History==
{{Main|Bus (computing)#History}}

Vacuum-tube based computers had modular construction, but individual functions for peripheral devices filled a cabinet, not just a printed circuit board. Processor, memory and I/O cards became feasible with the development of [[integrated circuit]]s.<ref>{{Cite web |title=Eurotherm Parker SSD Link Hardware L5341 {{!}} Automation Industrial |url=https://l5341.com/blog |access-date=2024-01-02 |website=l5341.com |language=en}}</ref> Expansion cards make processor systems adaptable to the needs of the user by making it possible to connect various types of devices, including I/O, additional memory, and optional features (such as a [[floating point unit]]) to the central processor. Minicomputers, starting with the [[PDP-8]], were made of multiple cards communicating through, and powered by, a passive [[backplane]].

The first commercial [[microcomputer]] to feature expansion slots was the [[Micral|Micral N]], in 1973. The first company to establish a [[de facto standard|''de facto'' standard]] was Altair with the [[Altair 8800]], developed 1974–1975, which later became a multi-manufacturer standard, the [[S-100 bus]]. Many of these computers were also passive backplane designs, where all elements of the computer, (processor, memory, and I/O) plugged into a card cage which passively distributed signals and power between the cards.

Proprietary [[bus (computing)|bus]] implementations for systems such as the [[Apple II]] co-existed with multi-manufacturer standards.

===IBM PC and descendants===
[[IBM]] introduced what would retroactively be called the [[Industry Standard Architecture]] (ISA) bus with the IBM PC in 1981. At that time, the technology was called the '''PC bus'''. The [[IBM Personal Computer XT|IBM XT]], introduced in 1983, used the same bus (with slight exception). The 8-bit PC and XT bus was extended with the introduction of the IBM AT in 1984. This used a second connector for extending the address and data bus over the XT, but was backward compatible; 8-bit cards were still usable in the AT 16-bit slots. Industry Standard Architecture (ISA) became the designation for the IBM AT bus after other types were developed. Users of the ISA bus had to have in-depth knowledge of the hardware they were adding to properly connect the devices, since memory addresses, I/O port addresses, and DMA channels had to be configured by switches or jumpers on the card to match the settings in driver software.

IBM's [[Micro Channel architecture|MCA]] bus, developed for the PS/2 in 1987, was a competitor to ISA, also their design, but fell out of favor due to the ISA's industry-wide acceptance and IBM's licensing of MCA. EISA, the 32-bit extended version of ISA championed by [[Compaq]], was used on some PC motherboards until 1997, when Microsoft declared it a "legacy" subsystem in the [[PC 97]] industry white-paper. Proprietary local buses (q.v. Compaq) and then the [[VESA Local Bus]] Standard, were late 1980s expansion buses that were tied but not exclusive to the 80386 and 80486 [[Central processing unit|CPU]] bus.<ref>{{cite web|url=http://www.artofhacking.com/th99/m/U-Z/32626.htm |title=MB-54VP |archive-url = https://web.archive.org/web/20130516025559/http://www.artofhacking.com/th99/m/U-Z/32626.htm|website= ArtOfHacking.com |access-date=|archive-date = 16 May 2013}}</ref><ref>{{cite web|url=http://www.artofhacking.com/th99/m/A-B/34897.htm |title=NX586 |website=ArtOfHacking.com |access-date=|archive-date = 16 May 2013|archive-url = https://web.archive.org/web/20130516063438/https://artofhacking.com/th99/m/A-B/34897.htm}}</ref><ref>{{cite web |url=http://www.artofhacking.com/th99/m/A-B/32775.htm |title=LEOPARD 486SLC2 REV. B |website=ArtOfHacking.com |access-date=2012-11-17 |archive-date=2014-10-17 |archive-url=https://web.archive.org/web/20141017222554/http://artofhacking.com/th99/m/A-B/32775.htm |url-status=dead }}</ref> The [[PC/104]] bus is an [[wikt:embedded|embedded]] bus that copies the ISA bus.

Intel launched their [[PCI bus]] chipsets along with the [[Pentium (original)|P5]]-based [[Pentium]] CPUs in 1993. The [[Peripheral Component Interconnect|PCI]] bus was introduced in 1991 as a replacement for ISA. The standard (now at version 3.0) is found on PC motherboards to this day. The PCI standard supports bus bridging: as many as ten daisy-chained PCI buses have been tested. [[CardBus]], using the [[PC Card|PCMCIA]] connector, is a PCI format that attaches peripherals to the Host PCI Bus via PCI to PCI Bridge. Cardbus is being supplanted by [[ExpressCard]] format.

[[Intel]] introduced the [[Accelerated Graphics Port|AGP]] bus in 1997 as a dedicated video acceleration solution. AGP devices are logically attached to the PCI bus over a PCI-to-PCI bridge. Though termed a bus, AGP usually supports only a single card at a time ([[Legacy system|Legacy]] [[BIOS]] support issues). From 2005 [[PCI Express]] has been replacing both PCI and AGP. This standard, approved{{Like whom?|date=May 2013}} in 2004, implements the logical PCI protocol over a serial communication interface. PC/104(-Plus) or [[Mini PCI]] are often added for expansion on small form factor boards such as [[Mini-ITX]].

For their [[Tandy 1000|1000 EX]] and [[Tandy 1000|1000 HX]] models, Tandy Computer designed the PLUS expansion interface, an adaptation of the XT-bus supporting cards of a smaller form factor. Because it is electrically compatible with the XT bus (a.k.a. 8-bit ISA or XT-ISA), a passive adapter can be made to connect XT cards to a PLUS expansion connector. Another feature of PLUS cards is that they are stackable. Another bus that offered stackable expansion modules was the "sidecar" bus used by the IBM [[IBM PCjr|PCjr]]. This may have been electrically comparable to the XT bus; it most certainly had some similarities since both essentially exposed the 8088 CPU's address and data buses, with some buffering and latching, the addition of [[interrupt]]s and [[Direct memory access|DMA]] provided by Intel add-on chips, and a few system [[fault (technology)|fault]] detection lines (Power Good, Memory Check, I/O Channel Check). Again, PCjr sidecars are not technically expansion cards, but expansion modules, with the only difference being that the sidecar is an expansion card enclosed in a plastic box (with holes exposing the connectors).

===External expansion buses===
Laptops are generally unable to accept most expansion cards intended for desktop computers. Consequently, several compact expansion standards were developed. 

The original [[PC Card]] expansion card standard is essentially a compact version of the ISA bus. The [[CardBus]] expansion card standard is an evolution of the PC card standard to make it into a compact version of the PCI bus. The original [[ExpressCard]] standard acts like it is either a USB 2.0 peripheral or a PCI Express 1.x x1 device. ExpressCard 2.0 adds SuperSpeed USB as another type of interface the card can use. Unfortunately, CardBus and ExpressCard are vulnerable to [[DMA attack]] unless the laptop has an IOMMU that is configured to thwart these attacks.

One notable exception to the above is the inclusion of a single internal slot for a special reduced size version of the desktop standard. The most well known examples are [[Mini-PCI]] or [[Mini PCIe]]. Such slots were usually intended for a specific purpose such as offering "built-in" wireless networking or upgrading the system at production with a discrete GPU.

===Other families===
Most other computer lines, including those from [[Apple Inc.]], [[Tandy Corporation|Tandy]], [[Commodore International|Commodore]], [[Amiga]], and [[Atari, Inc.]], offered their own expansion buses. The [[Amiga]] used [[Amiga Zorro II|Zorro II]]. Apple used a proprietary system with seven 50-pin-slots for [[Apple II peripheral cards]], then later used both variations on [[Processor Direct Slot]] and [[NuBus]] for its Macintosh series until 1995, when they switched to a PCI Bus.

Generally speaking, most PCI expansion cards will function on any [[Central processing unit|CPU]] platform which incorporates PCI bus hardware provided there is a software driver for that type. PCI video cards and any other cards that contain their own [[BIOS]] or other ROM are problematic, although video cards conforming to VESA Standards may be used for secondary monitors. DEC Alpha, IBM PowerPC, and NEC MIPS workstations used PCI bus connectors.<ref>{{cite web|url=http://www.artofhacking.com/th99/index.htm#1|title=Motherboards |publisher= Artofhacking.com|access-date=|archive-url = https://web.archive.org/web/20130516040936/https://artofhacking.com/th99/index.htm#1|archive-date = 16 May 2013}}</ref> Both Zorro II and NuBus were [[plug and play]], requiring no hardware configuration by the user.

Other computer buses were used for industrial control, instruments, and scientific systems. One specific example is HP-IB (or Hewlett Packard Interface Bus) which was ultimately standardized as [[IEEE-488]] (aka GPIB). Some well-known historical standards include [[VMEbus]], [[STD Bus]], [[SBus]] (specific to Sun's SPARCStations), and numerous others.

===Video game consoles===

Many other [[Video game console|video game consoles]] such as the [[Nintendo Entertainment System]] and the [[Sega Genesis]] included expansion buses in some form; In the case of at least the Genesis, the expansion bus was proprietary. In fact, the cartridge slots of many cartridge-based consoles (not counting the [[Atari 2600]]) would qualify as expansion buses, as they exposed both read and write capabilities of the system's internal bus. However, the expansion modules attached to these interfaces, though functionally the same as expansion cards, are not technically expansion cards, due to their physical form.