What is mca bus ISA bus VESA bus PCI bus?

ISA bus was a standard used for years. It was first 8-bit, being the standard expansion slot for most 8086/8088 motherboards, but later extended to 16-bit, which was the standard for 286, 386, and 486 motherboards. Most standard PC's had ISA slots through the late 1990's. They began to be phased out in the early 2000's, and are now obsolete.

VESA Local bus was an extension of the standard 16-bit ISA bus, and gave a 32-bit expansion slot. These were seen in late 486 and early Pentium motherboards, which would often have two or three VESA Local Bus slots in addition to 16-bit ISA slots. They were short lived, quickly replaced by PCI slots.

PCI was introduced in the mid 1990's, and are still common today. Some late 486 motherboards had two or three PCI slots in addition to 16-bit ISA slots, and they became standard with Pentium systems (most Pentium motherboards, Pentium II motherboards, and some Pentium III motherboards still had some ISA slots in addition to the PCI slots).

MCA was bus developed by IBM and used in their PS/2 systems. It is to buses what Beta is to the VCR: A good technology, but made obsolete because it's developers made it too expensive for other manufacturers to license. MCA offered a 32-bit bus before VESA Local Bus or PCI were available.