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Definition: ISA bus

(Industry Standard Architecture bus) An earlier hardware interface for connecting peripheral devices in PCs. Pronounced "eye-suh," ISA accepted cards for sound, display, hard drives and other devices. 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.

ISA Slots
This diagram shows a motherboard with three 16-bit ISA slots.

Mixed ISA Slots
Motherboards came with a mix of 8-bit (left) and 16-bit (right) slots such as this one.

Earlier Expansion Cards
Except for the PCI bus, ISA, AGP, EISA, Micro Channel and VL-bus have all disappeared.