ISA stands for Industry Standard Architecture. In IBM compatible computers it is the industry standard BUS. A bus is a subsystem that transfers data or power between computer components inside a computer, and typically is controlled by device driver software. Very low performance began as a 8-bit system initially developed by IBM in 1981. In 1983 a faster 16-bit architecture was developed called the XT bus architecture. The 8-bit bus ran at 4.77 MHz, while the 16-bit bus operated at 8 MHz. IBM in a bold move in 1987 developed yet another architecture the MCA Micro Channel Architecture in an attempt to take back control of the PC architecture, and market.
This was a system was more advanced then the ISA . But, other computer manufactures in response to IBM MSA also developed there own designed called EISA which stands for Extended Industry Standard Architecture.
Although it was even more advanced than the MSA running at 32 bits and was able to access up 4gb of memory it’s favor and popularity never developed. In 1990 Intel began work on a new design called the PCI Peripheral Component Interconnect, it is still being used today, and has become an industry standard One of the reasons that the PCI became and is still very popular today was the it was user friendly or just about any device you installed in the slot was plug and play.
ISA based machines were more difficult to configure in the since that, users needed to know and understand IRQ lines ,I/O address or better yet DMA address. IBM realized the problem with ISA slot, so response add a extra element to the slot calling it ISA PnP, it was designed to make it simpler to configure devices installed in the slot, but the designed flailed and later was referred to as the plug and pray architecture.
PCI slots were the first physically-incompatible expansion ports to directly squeeze ISA off of the motherboard. At first, motherboards were largely ISA, including a few PCI slots. By the mid-1990s, the two slot types were roughly balanced, and ISA slots soon were in the minority on consumer systems.
Microsoft's PC 97 specification recommended that ISA slots be removed entirely, though the system architecture still required ISA to be present in some vestigial way internally to handle the floppy drive, serial ports, etc. ISA slots remained for a few more years, and it was even possible to see systems with an Accelerated Graphics Port (AGP) sitting near the central processing unit, an array of PCI slots, and one or two ISA slots near the end.
It is also notable that PCI slots are "rotated" compared to their ISA counterparts—PCI cards were essentially inserted "upside-down," allowing ISA and PCI connectors.
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