The VAXBI bus (VAX Bus Interconnect bus) is a computer bus designed and sold by the

Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president un ...

(DEC) of

Maynard, Massachusetts Maynard is a town in Middlesex County, Massachusetts, United States. The town is located 22 miles west of Boston, in the MetroWest and Greater Boston region of Massachusetts and borders Acton, Concord, Stow and Sudbury. The town's population ...

. The bus is an advanced, configuration-free synchronous bus used on DEC's later

VAX VAX (an acronym for Virtual Address eXtension) is a series of computers featuring a 32-bit instruction set architecture (ISA) and virtual memory that was developed and sold by Digital Equipment Corporation (DEC) in the late 20th century. The V ...

computers. Like the

Unibus The Unibus was the earliest of several computer bus and backplane designs used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation (DEC) of Maynard, Massachusetts. The Unibus was developed around 1969 by Gordon ...

and

Q-Bus The Q-bus,Schmidt, Atlant G.,Unibus,Q-Bus and VAXBI Bus, in ''Digital bus handbook'', Di Giacomo Joseph Ed., McGraw Hill, 1990 also known as the LSI-11 Bus, is one of several bus technologies used with PDP and MicroVAX computer systems previo ...

before it, it uses

memory-mapped I/O Memory-mapped I/O (MMIO) and port-mapped I/O (PMIO) are two complementary methods of performing input/output (I/O) between the central processing unit (CPU) and peripheral devices in a computer. An alternative approach is using dedicated I/O pr ...

but has 32-bit address and data paths. The VAXBI is a multiplexed bus with fully distributed arbitration and geographic addressing. All of the logic required to implement a VAXBI interface is contained within a single custom integrated circuit (the "BIIC") and the physical layout and printed wiring board layout for compliant cards is tightly specified, right down to the location of the dual amber status LEDs that are required. The portion of the card that is reserved for the bus interface is referred to as "the VAXBI corner". VAXBI licensees were given the appropriate engineering drawings to allow them to exactly replicate a compliant card. VAXBI cards mount into backplanes using a

ZIF ZIF, ZiF or Zif may refer to: * Zero insertion force Zero insertion force (ZIF) is a type of IC socket or electrical connector that requires very little (but not literally zero) force for insertion. With a ZIF socket, before the IC is inserte ...

connector; depending on the backplane design, cards can be loaded from the top or the front side of the backplane. No cable connections are permitted on the cards; all connections are made via three uncommitted rows of backplane connectors. Similarly, no configuration jumpers are permitted on the cards; all setup is done by jumpers inserted on the backplane connectors or via software configuration. Originally conceived by its engineers to be an

open Open or OPEN may refer to: Music * Open (band), Australian pop/rock band * The Open (band), English indie rock band * ''Open'' (Blues Image album), 1969 * ''Open'' (Gotthard album), 1999 * ''Open'' (Cowboy Junkies album), 2001 * ''Open'' ( ...

bus, it was forced to be a tightly licensed bus by Digital's marketing and management, and was not nearly as successful as had originally been hoped-for. It is used in the

VAX 6000 The VAX 6000 is a discontinued family of minicomputers developed and manufactured by Digital Equipment Corporation (DEC) using processors implementing the VAX instruction set architecture (ISA). Originally, the VAX 6000 was intended to be a mid-ra ...

VAX 8000 The VAX 8000 is a discontinued family of superminicomputers developed and manufactured by Digital Equipment Corporation (DEC) using processors implementing the VAX instruction set architecture (ISA). The 8000 series was introduced in October 1 ...

(82xx, 83xx, 85xx, 87xx, 88xx models) and the

VAX 9000 The VAX 9000 is a discontinued family of Minicomputers developed and manufactured by Digital Equipment Corporation (DEC) using custom ECL-based processors implementing the VAX instruction set architecture (ISA). Equipped with optional vector p ...

systems and also on the MIPS R3000 based

DECsystem DECsystem was a line of server computers from Digital Equipment Corporation. They were based on MIPS architecture processors and ran DEC's version of the UNIX operating system, called ULTRIX. They ranged in size from workstation-style desktop enc ...

5800 series. A PDP-11 implementation (the PDP-11/27) was envisioned but never advanced beyond the concept stage.

References

Computer buses DEC hardware Minicomputers {{mini-compu-stub