A brisk frisk with CISC & RISC

by Reggie Huff

This past weekend I found myself sitting next to the cooler, watching my Brother Wildman navigate the flames as he barbecued our dinner. He looked up at me and said "Brother, git me beer, will ya?" (He's from Texas.)

Cleary a simple request to interpret. A simple project to execute.

Neither of us noticed at the time, but there was a true invisible complexity suffusing the entire matter. Furthermore, that invisible complexity consisted of two very distinct domains: Interpretation and Execution.

Interpretation was the easy part, because Wildman and I share a pretty well established Background of Obviousness. For example, I instantly concluded that:
• He wanted the beer cold not warm
• He'd prefer it to be fresh and clean (not handed to him in the half-filled glass with the cigarette butt in it) He sought a can, or bottle, or glass of it (not a case, a keg, a palette, or a barrel of beer)
• He wanted it to be delivered within the next few minutes (not in the next few weeks or months)

Even though he IS from Texas, I was quite confident that I had correctly interpreted his instruction and that, if I could execute the task, the whole thing would be a success.

The hard part of navigating the invisible complexity was in the Execution. What at first seemed to be a very simple instruction-especially since I was already sitting next to the cooler- was, as it turns out, far more complex than I had ever imagined.

You see, this "Git beer" project ultimately amounted to a very complex sequence of steps in which I would send a single signal down a nerve to cause a muscle to contract or relax. An extremely simplified beginning to the myriad steps might include rotating my head to the left to view the cooler.

This in turn would have required me to:
• send a signal to contract the left horizontal control muscles for each eye
• send a signal to relax the right horizontal control muscles for each eye
• send a signal to contract the left neck muscles
• send a signal to relax the right neck muscles

As I rotated my upper torso to begin my lean toward the cooler, I would have needed to: send a signal to my upper left back muscle Etc.

CISC is an acronym for Complex Instruction-Set Computing. RISC is an acronym for Reduced Instruction-Set Computing.

Both CISC and RISC instructions must be interpreted and then broken down into a sequence of steps (like "Turn this transistor on" or "Turn that transistor off") that will allow the computer to perform its task.

"Turn this transistor on," and "Turn that transistor off" are the computer equivalent of "Send a signal to contract this muscle," and "Send a signal to relax that muscle." When the original program finally gets translated all the way down to its basic sequence of 1's and 0's, the format is called Machine Language.

CISC processors are designed to accept very high level (Complex) instructions. They then break these instructions down into the many constituent steps necessary to execute the instruction...and that interpretation takes time.

Most available microprocessors are CISC type:

RISC processors are optimized to accept less complex (Reduced) instructions. Since these reduced instructions take less time to interpret down to machine language, each instruction can be executed more quickly. The downside is that it takes many more of these reduced instructions in the program to accomplish the same task that you could specify with a single-line complex instruction.

RISC processors you may be familiar with include:

Wildman gave me a complex instruction with his one liner "Brother, git me beer, will ya?" Had he been using reduced instructions, he might have told me to:

• Reach out to the cooler with your left arm
• Grasp the leading edge of the cooler top
• Move the cooler top to its opened position
• Reach into the ice water and locate a can
• Grasp the can and retract your arm
• Etc.

With CISC processors, the programs are MUCH shorter and each line in the program takes MUCH longer to interpret and execute. With RISC processors, the programs (sometimes called the Application Program) require many, many more instruction lines but each instruction gets executed much more quickly.

Until recently, all personal computers utilized CISC processors, and RISC processors were reserved for higher-performance workstations. That changed with the introduction of the PowerPC processor. The PowerPC constitutes a family of RISC processors that are inexpensive enough to integrate into personal computers.

You may have noticed that they didn't really provide much performance improvement until application software companies were able to provide the Native upgrade of their software. Once they converted their program code from the Complex Instruction Set to the Reduced Instruction Set, personal computer performance soared.

"A Brisk Frisk With CISC & RISC" first appeared on EBNONLINE.COM on September 13, 1999.

© Copyright 1999, 2000, 2001 Huff Communications. All Rights Reserved.