Microprogramming heritage of RISC design

The paper summarizes the current design trends of micro-architectures and analyzes the tradeoffs between the RISC approach and the microprogramming approach especially on vertical migration among hardware, firmware, compilation, and software. RISCs simplicity is contrasted by the regularity of microprogrammed control. The RISC design incentives are categorized into three perspectives, namely, technology-driven, application-driven, and performance-driven. Traditional firmware migration approaches are reviewed and related to the RISC design philosophy as well as, the writable instruction set computer (WISC) concept. Research such as firmware migration candidates selection can be applied to RISC instruction set design. Similarly, micro-code generation and compaction research can be used to construct smart, optimizing RISC compilers. Horizontal microcoding is interpreted by the very long instruction word (VLIW) architecture