The Weitek's were memory mapped. (At least those built for x86 machines.).
This essentially increased bandwidth by using the address bus as a source for floating point instructions. Was really a very cool idea, although I don't know what the performance realities were when using one.
http://www.bitsavers.org/components/weitek/dataSheets/WTL-31...
The operand fields of a WTL 3167 address have been specifically designed so that a WTL 3167 address can be given as either the source or the destination to a REP MOVSD instruction. [
Single-precision vector arithmetic is accomplished by applying the 80386 block move instruction REP MOVSD to a WTL 3167 address involving arithmetic instead of loading or storing.
iirc the 3167 was a single clocked, full barrel shift mac pipeline with a bunch (64?) of registers, so the FPU could be driven with a RISC-style opcode on every address bus clock (given the right driver on the CPU) ... the core registers were enough to run inner loops (think LINPACK) very fast with some housekeeping on context switch of course
this window sat between full PCB minicomputer FPUs made from TTL and the decoupling of microcomputer internal clocks & cache from address bus rates ...
Weitek tried to convert their FPU base into an integrated FPU/CPU play during the RISC wars, but lost