An expansion card in computing is a printed circuit board that can be inserted into an expansion slot of a computer motherboard to add additional functionality to a computer system.

One edge of the expansion card holds the contacts that fit exactly into the slot. They establish the electrical contact between the electronics (mostly integrated circuits) on the card and on the motherboard.

Connectors mounted on the bracket allow the connection of external devices to the card. Depending on the form factor of the motherboard and case, around one to seven expansion cards can be added to a computer system. There are also other factors involved in expansion card capacity. For example, some expansion cards need two slots like some NVidia GeForce FX graphics cards and there is often a space left to aid cooling on some high end cards.

History of the expansion card

The first microcomputer to feature a slot-type expansion card bus was the Altair 8800, developed 1974-1975. Initially, implementations of this bus were proprietary, but by 1982 manufactureres had settled around the S-100 standard. IBM introduced the XT bus with the first IBM PC in 1983. XT was replaced with ISA in 1984. IBM's MCA bus, developed for the PS/2 in 1987, was a competitor to ISA, but fell out of favor due to the latter's industry-wide acceptance. EISA, the 16-bit extended version of ISA, was common on PC motherboards until 1997, when Microsoft declared it as "legacy" subsystem in the PC 97 industry white-paper. VESA Local Bus, an early expansion bus that was inherently tied to the 80486 CPU, became obsolete (along with the processor) when Intel launched the Pentium processor in 1996.

The PCI bus was introuduced in 1991 as replacement for ISA. The standard (now at version 2.2) is still found on PC motherboards to this day. Intel introduced the AGP bus in 1997 as a dedicated video acceleration solution. Though termed a bus, AGP supports only a single card at a time. Both of these technologies are now slated to be replaced by PCI-Express, beginning in 2005. This latest standard, approved in 2004, implements the logical PCI protocol over serial communication interface.

Expansion slot standards

• PCI Express
• AGP
• PCI
• ISA
• MCA
• VLB
• XT
• PCMCIA (Notebook computers)

Expansion card types

• Graphics card
• Sound card
• Network card
• TV card
• Modems
• Wireless network (such as WiFi) cards.
• Hard disk/RAID controllers
• POST cards