RISC vs. CISC: The Real Story
What makes the PowerPC a RISC processor and the Pentium a CISC?
By Jeff Prosise
The recent emergence of PowerPC-based computers as serious contenders in a marketplace dominated by Intel has stoked the fires of a great debate. Which is better: RISC (reduced instruction-set computing) or CISC (complex instruction-set computing)? RISC backers contend that their chips run faster and are generally more powerful than CISC chips, but Intel and other CISC proponents adamantly oppose this view.
What's missing from the debate is a discussion of the actual differences between RISC and CISC chips. Reduced instruction set would seem to imply that RISC processors support fewer instructions than their CISC counterparts. But is this really the case? And if it is, wouldn't that mean that a RISC processor runs software more slowly, since it has to execute more instructions to carry out complex tasks such as recalculating cells in a large spreadsheet or drawing a graphical image on-screen? What, if anything, is the advantage of a smaller instruction set? And just what is an instruction set, anyway?
In the interest of a more informed debate, the following discussion seeks to answer these questions and outline exactly what it is that makes a processor RISC or CISC. If you don't know the answer already, the truth may surprise you.
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Published as Tutor in the 10/24/95 issue of PC Magazine.
