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According to Wikipedia, x86 is a CISC design, but I also have heard/read that it is RISC. What is correct? I'd to also like to know why it is CISC or RISC. What determines if a design is RISC or CISC? Is it just the number of machine language instruction a microprocessors has or are there any other characteristics that determine the architecture?
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RISC-V and ARM processors are based on RISC concepts in terms of computing architectures, while x86 processors from Intel and AMD employ CISC designs. A RISC architecture has simple instructions that can be executed in a single computer clock cycle.
Intel's x86's do NOT have a RISC engine “under the hood.” They implement the x86 instruction set architecture via a decode/execution scheme relying on mapping the x86 instructions into machine operations, or sequences of machine operations for complex instructions, and those operations then find their way through the ...
The x86 architecture is a variable instruction length, primarily "CISC" design with emphasis on backward compatibility. The instruction set is not typical CISC, however, but basically an extended version of the simple eight-bit 8008 and 8080 architectures.
The Intel x86/x64 architecture(s) are definitely CISC.
x86 is a CISC architecture. The number of instructions is a big factor as all cisc architectures with all more instructions. Furthermore as instructions are complex in cisc they can take >1 cycle to complete, where as in RISC they should be single cycle. The main differences are found here:
+------------------------------+------------------------------+ | CISC | RISC | +------------------------------+------------------------------+ | Emphasis on hardware | Emphasis on software | | . | | | Includes multi-clock | Single-clock, | | complex instructions | reduced instruction only | | . | | | Memory-to-memory: | Register to register: | | "LOAD" and "STORE" | "LOAD" and "STORE" | | incorporated in instruction | are independent instructions | | . | | | Small code sizes, | Low cycles per second, | | high cycles per second | large code sizes | | . | | | Transistors used for storing | Spends more transistors | | complex instructions | on memory registers | +------------------------------+------------------------------+
For further research consult here: http://www-cs-faculty.stanford.edu/~eroberts/courses/soco/projects/risc/risccisc/
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