|MadSci Network: Computer Science|
Reply From: Mike Westerfield Byte Works, Inc. Your question seems simple on the surface, but it's sort of like asking "What's the fastest, cheapest car?" Like a car, faster generally means more expensive when you talk about computers. Also like a car, fast means different things. A car built for drag racing would get killed in the Indianapolis 500, and both a drag racer and an Indy 500 race car would be slower than the family van getting to the grocery store because there is so much involved in getting them going! Computers are the same. If your task is sorting census data for the upcoming U.S. census, you need a computer that is very fast at simple logical operations and comparing values. As we'll see in a moment, the best computer for that task won't be the same one as the best computer for complex filters in PhotoShop. In fact, the only reliable way to tell which computer will be fastest for a particular job is to try that job on each computer. That's what benchmarks do. The Spec Benchmarks In general, there are two kinds of speed we measure on computers, integer math and logic, and floating point. The most common benchmark for integer math and logic is the Spec Int 95 benchmark, which is actually made up of several programs. The final grade is a number, and the bigger the number the better the processor did. The Spec Int 95 benchmark gives you a good idea how a processor will do on jobs like the U.S. census. Floating-point speed is measured by the Spec FP 95 benchmark. Just like the Spec Int 95 benchmarks, this is really a group of programs, and a bigger number is better. This benchmark gives you an idea how a processor will do on jobs like PhotoShop filters, spreadsheets, or predicting hurricanes. Rating a Few Common Processors Here's a table showing a few common modern microprocessors, along with their Spec benchmarks and a rough estimate of price. If the table seems messed up, change the font to a monospaced font like Courier. Chip Speed (MHz) Price Spec Int Spec FP ---- ----------- ----- -------- ------- Pentium III 450 $183 18.7 13.7 Pentium III 600 $869 24.9 (est) 18.3 (est) Pentium II 450 $183 18.5 11.9 PowerPC G4 450 $355 21.4 20.4 Celeron 500 $204 17.9 12.9 Alpha 21164 533 16.1 22.5 Looking at this chart, you can see how much you pay for speed. The Pentium III at 600 MHz costs almost 5 times as much as one running at 450 MHz, but only runs about 1.3 times as fast! You can also start to see through some of the hype surrounding processor speed. The makers of the Alpha 21164 claim it's the fastest chip going--and for floating-point calculations, they have some support for their claim. But most people don't do floating-point, and look at how it does on the more common integer operations! The Chip Isn't the Whole Story For most applications, there is a lot more going on than the processor speed. Comparing two computers isn't the same thing as comparing the processors inside the computers! It doesn't matter much how fast the processor is if your job is copying files from one disk to another--it's the speed of the disks that matter. A lot of the time you spend on a computer depends more on the speed of your disk drives and modem than on the microprocessor. Making it Cheaper If you're going to build something yourself, maybe a home-brew robot, there are lots of ways to make your computer cheaper. The modern processors you see in the chart are big, expensive chips. A robot wouldn't need them. In fact, you can probably get the microprocessor for free! As just one example, a lot of school closets are full of old Apple II computers that are being thrown away. Pull the 6502 microprocessor out and use it in your project, and you have a very reasonable microprocessor for the task for nothing. Even if you need to buy a microprocessor, there are all sorts of specialized chips that cost lots less than the ones in the table. Some are rip-offs of the Pentium that run a little slower. Some, like the BASIC Stamp, are complete computers on a chip, designed for projects like building a Robot. Making it Faster If you're NASA, trying to build a faster computer to simulate air flowing over an airplane wing, there is another way to make your computer faster. Instead of using one microprocessor, why not use two? Or four? Or 1,024? That's called parallel computing, and it's exactly what big government agencies do. They build specialized computers that are really more than one computer inside, and program the machine so all of the computers work on different parts of the same problem. Parallel computing is expensive, but very fast. Sandia National Laboratories did the race car equivalent of breaking the sound barrier last year using a parallel computer when they broke the terraFLOPS barrier. Their computer did a little over 1,000,000,000,000 floating-point operations in one second! Another way to get lots of speed is by adding an extra processor for doing specialized calculations. That's what Apple did in their new PowerMac G4. Their microprocessor is impressive on its own, outrunning the best Windows based machines, but it's not three times faster like Apple's ads claim. The way they got the extra speed was by adding a vector processor, which is a special microprocessor that does some kinds of calculations blindingly fast. It really won't do much for sorting a database, but if you are using PhotoShop or doing scientific calculations, it screams. Apple claims that on problems like those, the new computer does 1,000,000,000 floating point operations per second--and it can go even faster in some cases. Times are Changing The speed you see today will seem slow when you graduate from High School. When I was in college, mumble-mumble years ago, the Cray 1 was the speed king. It was a big, expensive computer that needed a room, special liquid coolant, and a staff of people to keep it going. It's speed was about 100,000,000 floating-point operations per second. It seems pretty slow these days! Summary So, Joe, as you see, your question wasn't as simple as you thought! If you want speed, you have to shell out lots of money. There are different kinds of speed, too, so you need to be careful to choose the machine that is fast the way it matters to you. And if cost is more important than speed, there are lots of ways to cheat the system, sometimes so much that you get your microprocessor for free. References http://www.specbench.org/ http://www.ugeek.com/procspec/procspec.htm http://www.alpha-processor.com/ http://www.intel.be/procs/perf/celeron/ http://www.apple.com/ http://mot-sps.com/
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