At the time it was developed Futurebus+ was probably the most advanced and highest performance bus. It had very advanced protocols that did a great job of handling distributed cache coherency, and a very nice distributed priority resolution circuitry. DEC could have build a complete VAX or Alpha on Futurebus+ and made a very high performance system. SCI (Scalable Coherent Interface) would be the best choice for interconnecting Futurebus+ systems. Unfortunately the NAVY's NGCR program, that was one of the big target markets for Futurebus+, was defunded and support for Futurebus+ evaporated. High speed serial buses were also getting fast enough to be competitive with parallel buses, and much easier to implement than a 64/128/256 bit wide bus. -- Michael Thompson