The MCA standard was designed to take the place of the AT and ISA buses used in previous IBM PC/AT compatible computers. While the MCA bus architecture was an improvement in both size and speed over AT and ISA, it was kept as a proprietary standard by IBM. This discouraged other manufacturers from adopting the standard, since the MCA architecture was not compatible with other standards. Most PC companies incorporated the more universal PCI and AGP expansion buses into their computers, which are both widely used today.