Competition for the bus at the time included IBM’s MicroChannel Architecture (MCA), introduced on their PS/2 personal computer systems and the EISA bus, promulgated by a PC manufacturers’ group.
MCA, unlike the open ISA bus, was a protected piece of IBM intellectual property; the result was that it only ever appeared in IBM products.
EISA suffered from a different problem; since it was backwards compatible with the venerable ISA bus, it embodied a number of compromises which limited its advantages over the earlier standard.
PCI won against both MCA and EISA through its combination of functionality and its openness.
Source of Information : Elsevier Server Architectures 2005