MIPS R4000 Microprocessor User's Manual 3
Introduction
Shorter Design Cycle
The architectures of RISC processors can be implemented more quickly
than their CISC counterparts: it is easier to fabricate and debug a
streamlined, simplified architecture with no microcode than a complex
architecture that uses microcode. CISC processors have such a long
design cycle that they may not be completely debugged by the time they
are technologically obsolete. The shorter time required to design and
implement RISC processors allows them to make use of the best available
technologies.
Effective Utilization of Chip Area
The simplicity of RISC processors also frees scarce chip geography for
performance-critical resources such as larger register files, translation
lookaside buffers (TLBs), coprocessors, and fast multiply and divide units.
Such resources help RISC processors obtain an even greater performance
edge.
User (Programmer) Benefits
Simplicity in architecture also helps the user by providing a uniform
instruction set that is easier to use. This allows a closer correlation
between the instruction count and the cycle count, making it easier to
measure code optimization activities.
Advanced Semiconductor Technologies
Each new VLSI technology is introduced with tight limits on the number
of transistors that fit on each chip. Since the simplicity of a RISC processor
allows it to be implemented in fewer transistors than its CISC counterpart,
the first computers capable of exploiting these new VLSI technologies
have been using and will continue to use RISC architecture.
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