(Industry Standard Architecture bus) A hardware interface for connecting peripheral devices in earlier PCs. Pronounced "eye-suh," ISA accepted plug-in cards for sound, display, hard drives and other connectivity. Originally called the "AT bus" and introduced with the IBM PC AT in 1984, the AT/ISA bus extended the PC bus from 8 to 16 bits. For several years, motherboards provided a mix of both 8-bit and 16-bit ISA slots. As PCI became popular, motherboards included only 16-bit ISA and PCI, and by the early 2000s, ISA was being replaced entirely by the PCI interface. See PC data buses and PCI.