The FPP8/A was a floating point processor, nominally for the PDP-8/A, but it can operate on any OMNIBUS PDP-8. it was not part of the CPU, but used DMA for its instructions and data.
Its floating point format provided three and six word formats, with 12 bits of exponent; it also supported double-word integers.
It used two hex boards, so to fit it into a machine that normally only holds quad boards (such as a PDP-8/M), one of the fans has to be removed. It has been observed to operate in a PDP-8/M, though.