(Extended ISA) Pronounced "ee-suh." A PC bus standard that extends the 16-bit ISA bus (AT bus) to 32 bits and provides bus mastering. ISA cards can plug into an EISA slot. It was announced in 1988 as a 32-bit alternative to the Micro Channel that would preserve investment in existing boards. However, EISA runs at the slow 8 MHz speed of the ISA bus in order to accommodate any ISA cards that may be plugged into it. EISA has been superseded by PCI. See PC data buses.