FASTBUS is a standardized specification that defines electronic modules that are used in nuclear and particle physics. It is defined by an IEEE standard (960) published in 1984. It was conceived as a replacement for CAMAC.
FASTBUS never saw widespread adoption. Most installations that required higher speed or greater flexibility than CAMAC could provide moved to VMEbus, and those installations remain common today.
The number and types of connectors on the front or rear of a FASTBUS module are entirely implementation-specific, i.e. they depend on what function the module is designed to perform.
Typical FASTBUS modules are counters, timing pulse generators, amplifiers, digitizers, digital memory (for use with digitizers), pulse-height analyzers for nuclear spectrometry, and many others.
LeCroy was the primary manufacturer of FASTBUS modules, though they were sold by other manufacturers as well. Like NIM and CAMAC, due to standardization, FASTBUS modules are interoperable between manufacturers.
At the time of this writing, FASTBUS modules are somewhat rare on the open market, but they occasionally appear in auction venues.