(EISA) /eesa/ A bus standard for IBM compatibles that extends the ISA bus architecture to 32 bits and allows more than one CPU to share the bus. The bus mastering support is also enhanced to provide access to 4 GB of memory. Unlike MCA, EISA can accept older XT bus architecture and ISA boards. EISA was announced in late 1988 by compatible vendors as a counter to IBM's MCA in its PS/2 series. Although somewhat inferior to the MCA it became much more popular due to the proprietary nature of MCA.