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Industry Standard Architecture (ISA) is a computer bus specification used for 8-bit IBM-compatible systems. An ISA bus provides a basic route for peripheral devices that are attached to a motherboard to communicate with different circuits or other devices that are also attached to the same motherboard.
Peripheral component interface (PCI) started replacing the ISA bus in the mid-’90s. New motherboards were manufactured with fewer ISA slots, and preference was given to PCI slots.
Techopedia Explains Industry Standard Architecture
Initially, an ISA bus was the best option for Intel machines. However, eventually a faster and wider bus was required, and an issue of incompatibility arose. The manufacturers relied on the same ISA bus but added 16-bit characteristics.
The new ISA bus was flexible in that it could connect multiple devices. It supported 16-bit peripheral devices. Therefore, five devices with 16-bit interrupt request (IRQ) could be connected at the same time. Also, three additional devices could be connected parallel to five devices with 16-bit IRQ and a 16-bit direct memory access (DMA) channel. The CPU clock speed varied from 16 to 20 MHz.
