Is x86 RISC or CISC?

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?

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/

The early x86's (8086 / 186 / 286 / 386) were definitely CISC.

However, more recent processors can be regarded as hybrid, with a RISC core

Additional reference here