<P> Companies like Dell improved the AT bus's performance but in 1987, IBM replaced the AT bus with its proprietary Micro Channel Architecture (MCA). MCA overcame many of the limitations then apparent in ISA but was also an effort by IBM to regain control of the PC architecture and the PC market . MCA was far more advanced than ISA and had many features that would later appear in PCI . However, MCA was also a closed standard whereas IBM had released full specifications and circuit schematics for ISA . Computer manufacturers responded to MCA by developing the Extended Industry Standard Architecture (EISA) and the later VESA Local Bus (VLB). VLB used some electronic parts originally intended for MCA because component manufacturers already were equipped to manufacture them . Both EISA and VLB were backwards - compatible expansions of the AT (ISA) bus . </P> <P> Users of ISA - based machines had to know special information about the hardware they were adding to the system . While a handful of devices were essentially "plug - n - play", this was rare . Users frequently had to configure parameters when adding a new device, such as the IRQ line, I / O address, or DMA channel . MCA had done away with this complication and PCI actually incorporated many of the ideas first explored with MCA, though it was more directly descended from EISA . </P> <P> This trouble with configuration eventually led to the creation of ISA PnP, a plug - n - play system that used a combination of modifications to hardware, the system BIOS, and operating system software to automatically manage resource allocations . In reality, ISA PnP could be troublesome and did not become well - supported until the architecture was in its final days . </P> <P> PCI slots were the first physically - incompatible expansion ports to directly squeeze ISA off 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 of consumer systems . Microsoft's PC 99 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., which was why the software compatible LPC bus was created . ISA slots remained for a few more years, and towards the turn of the century it was common 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 . In late 2008, even floppy disk drives and serial ports were disappearing, and the extinction of vestigial ISA (by then the LPC bus) from chipsets was on the horizon . </P>

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