VAXBI
| Company type | Bus architecture |
|---|---|
| Industry | Computer hardware |
| Founded | 1986 |
| Founder | Digital Equipment Corporation (DEC) |
| Products | Computer bus architecture |
VAXBI (short for VAX Bus Interconnect) is a computer bus architecture created and marketed by Digital Equipment Corporation (DEC), first introduced in 1986.
This bus represents a sophisticated, synchronous design that requires no configuration, utilized in DEC's subsequent VAX computer models. Similar to its predecessors, the Unibus and Q-Bus, it employs memory-mapped I/O, but distinguishes itself with 32-bit wide address and data paths. VAXBI operates as a multiplexed bus featuring fully distributed arbitration alongside geographic addressing.
The entire VAXBI interface logic is integrated into a single custom chip known as the "BIIC." Additionally, the physical and PCB layouts for compatible expansion cards are precisely defined, including the placement of dual amber status LED indicators. The designated bus interface section on each card is referred to as "the VAXBI corner." Licensees were provided with comprehensive engineering schematics to produce compliant cards exactly. Expansion cards connect to the backplane through ZIF connectors, allowing insertion either from the top or front depending on the backplane configuration. Cards do not contain cable connections or configuration jumpers; all setup occurs via backplane jumpers or software controls.
Although originally designed as an open bus, strict licensing policies imposed by Digital's marketing and management teams restricted its broader adoption in the market.
VAXBI found use in the VAX 6000, VAX 8000 series (including models 82xx, 83xx, 85xx, 87xx, 88xx), and VAX 9000 systems, as well as within the MIPS R3000-based DECsystem 5800 lineup.
A version for the PDP-11 platform (PDP-11/27) was proposed but never progressed beyond the conceptual phase.