Industry Standard Architecture

(redirected from PC-AT bus)

Industry Standard Architecture

(architecture, standard)
(ISA) A bus standard for IBM compatibles that extends the XT bus architecture to 16 bits. It also allows for bus mastering although only the first 16 MB of main memory is available for direct access. In reference to the XT bus architecture it is sometimes referred to as "AT bus architecture".

Compare EISA, MCA.
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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.
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