Microcoded

Also, the 80286 was more efficient in the prefetch of instructions, buffering, execution of jumps, and in complex microcoded numerical operations such as MUL DIV than its predecessor.

Comparison to VLIW and RISC The design trend toward heavily microcoded processors with complex instructions began in the early 1960s and continued until roughly the mid-1980s.

Contrary to popular simplifications (present also in some academic texts), not all CISCs are microcoded or have "complex" instructions.

It was also discovered that, on microcoded implementations of certain architectures, complex operations tended to be slower than a sequence of simpler operations doing the same thing.

Many I/O devices supported "microcoded" IOT instructions.

Microcoded actions took place in a well-defined sequence designed to maximize the utility of many combinations.

Modern VLSI processors instead use matrices of field-effect transistors to build the ROM and/or PLA structures used to control the processor as well as its internal sequencer in a microcoded implementation.

The MACSS team drew heavily on the influence of minicomputer processor design, such as the PDP-11 and VAX systems, which were similarly microcoded.

There are counterpoints as well: * The complex instructions in heavily microcoded implementations may not take much extra machine resources, except for microcode space.