Stands for "Industry Standard Architecture." ISA is a type of bus used in PCs for adding expansion cards. For example, an ISA slot may be used to add a video card, a network card, or an extra serial port. The original 8-bit version of PCI uses a 62 pin connection and supports clock speeds of 8 and 33 MHz. 16-bit PCI uses 98 pins and supports the same clock speeds.
The original 8-bit version of ISA was introduced in 1981 but the technology did not become widely used until 1984, when the 16-bit version was released. Two competing technologies -- MCA and VLB -- were also used by some manufacturers, but ISA remained the most common expansion bus for most of the 1980s and 1990s. However, by the end of the twentieth century, ISA ports were beginning to be replaced by faster PCI and AGP slots. Today, most computers only support PCI and AGP expansion cards.