Dammit, sorry .. that was RISC-II. "The other major change was to include an instruction-format expander, which invisibly "up-converted" 16-bit instructions in

Dammit, sorry .. that was RISC-II. "The other major change was to include an instruction-format expander, which invisibly "up-converted" 16-bit instructions into a 32-bit format. This allowed smaller instructions, typically things with one or no operands, like NOP, to be stored in memory in a smaller 16-bit format, and for two such instructions to be packed into a single machine word. The instructions would be invisibly expanded back to 32-bit versions before they reached the arithmetic logic unit (ALU), meaning that no changes were needed in the core logic. This simple technique yielded a surprising 30% improvement in code density, making an otherwise identical program on Blue run faster than on Gold due to the decreased number of memory accesses." https://en.wikipedia.org/wiki/Berkeley_RISC#RISC_II https://en.wikipedia.org/wiki/Berkeley_RISC#RISC_II