Industry standard architecture

Industry Standard Architecture (in practice almost always shortened to ISA) is a bus standard for IBM compatibles that extends the XT bus architecture to 16 bits. It is designed to connect peripheral cards to the motherboard. The protocols 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.

Since the late 1990s most IBM PC motherboards have been designed with several PCI slots and few or no ISA slots. System manufacturers often shield customers from the term 'ISA bus', referring to it instead as the legacy bus (see legacy system).

See also:

• Extended Industry Standard Architecture (which is a compatible extension)
• Micro Channel Architecture (which was IBM's failed attempt at introducing an incompatible but improved bus)
• Peripheral Component Interconnect (a popular incompatible improved bus)
• XT bus architecture (the predecessor)
• VESA Local Bus devised for quicker access to video devices.