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Quick, what pops into your head when you hear the name AMD? If you're like most people, you think of low-priced computers that aren't quite as fast as the more expensive Intel-based models. But AMD's new K6-III chip may force you to think again.

In our PC WorldBench tests, which measure PCs' performance on common desktop applications, the fastest K6-III PCs we tested this month--unlike the first K6-III model we tested last month--performed as well as Pentium IIIs that run at higher clock speeds. In other words, the fastest K6-III-400 performed like a Pentium III-450, and the fastest K6-III-450 performed like a Pentium III-500. Nevertheless, you should be able to find K6-III PCs selling for $300 to $600 less than comparable PIII systems.

But where speed matters most--multimedia and 3D graphics--the K6-III was a disappointment. In fact, our K6-III-450s ran as much as 44 percent slower than the average Pentium II-450 in our graphics tests.

The lowdown: For business use, the K6-III is within striking distance of the fastest machine you can buy, but it lacks power for serious game playing or complex graphics tasks like multimedia editing.

$1599 on Up

We checked out five K6-III systems, including two 400-MHz models, the $1599 CyberMax Enthusiast KIII-400 and the $1799 Micro Express MicroFlex K6-3/400. This Micro Express was the only shipping unit we tested; all others were preproduction models.

We tested the CyberMax last month, and it failed to perform like a PIII-450, but we couldn't make generalizations about the chip based on a single PC. This month, we had multiple systems to test and could draw more conclusions.

We also evaluated three 450-MHz systems this month. At the high end, the $2480 Compaq Presario 5600s-450 has a large, beautiful flat-panel display. The $1749 CyberMax Enthusiast KIII-450 was identical to the Enthusiast KIII-400 in all ways except clock speed. Finally, we upgraded the 400-MHz Micro Express to 450 MHz ourselves; Micro Express assured us that what we created was analogous to its own 450 machine.

In addition to the K6-III, AMD has released a new chip optimized for notebooks, the K6-2 Mobile. We looked at the first notebook to sport this chip, Toshiba's Satellite 2545XCDT. If this notebook's performance is any indication, the new mobile chip won't satisfy speed-hungry users.

Cache-22

The K6-III owes its terrific business performance to its cache--or more precisely, its caches. All processors since the Pentium MMX have come with a 64KB level 1 cache built into the chip itself. The Pentium II and III supplement this with a 512KB level 2 cache that sits right next to the chip on the same cartridge and operates at half the chip's speed. The Celeron has a 128KB cache on the chip itself that's a quarter the size of the Pentiums', but it runs at the same speed as the chip.

Note: We incorrectly stated the amount of level 1 cache on all Intel processors since the Pentium MMX. The Pentium MMX, Pentium II, and Pentium III processors come with a 32KB level 1 cache. (This paragraph was added on June 7, 1999, to correct the error.)

The K6-III has all these beat. In addition to the 64KB of L1 cache, the chip includes 256KB of L2 cache on the chip, where, like the Celeron's cache, it operates at full speed. The chip also supports a third level of cache on the motherboard, but only if the system manufacturer chooses to put one there.

The smart ones will. Three of the five systems we tested had 1MB L3 caches, and these were the star performers. The 450-MHz Compaq and Micro Express PCs scored over 225 on WorldBench--comparable to the average Pentium III-500 system. (The fastest Pentium III-500 scored a slightly higher 237.) The 400-MHz Micro Express scored 217 on our benchmark tests, only a hair behind the PIII-450s' average of 219. That's great performance, particularly when you consider that you're paying hundreds of dollars less for it.

On the other hand, the 400- and 450-MHz CyberMax systems came with only 512KB each of L3 cache, which probably contributed to their lower PC WorldBench scores of 202 and 212, respectively. Still, these machines provide plenty of speed for all but the most demanding of users.

Graphic Disappointment

The K6-III may be a killer at standard business applications, but when you run the latest 3D shoot-'em-up, you could be the victim. In PC World's graphics benchmarks, the K6-III-450 PCs that had been running like Pentium III-500s couldn't keep up with the average PII-450.

On the PowerPoint test, our least taxing graphics test, the K6-III systems came within striking distance of the Pentium IIIs. The CyberMax K6-III-450, the slowest K6-III-450 in our business application tests, finished this test in 156 seconds, only 9 seconds behind the average Pentium III-500 with the same NVidia TNT graphics chip.

The K6-III systems were significantly slower on our more demanding graphics tests. For example, in the Redline Racer game test, Compaq's pricey Presario 5600s-450 ran about 44 percent slower than the average similarly configured PII-450 PC we've tested. On the same test, the 450-MHz CyberMax Enthusiast fared only slightly better, trailing the PII-450s by about 30 percent. On the Director test, results were similarly unimpressive: The top-performing Compaq lagged behind the Pentium II-450s by about 11 percent.

The 400-MHz Micro Express ran as fast as or faster than the quickest K6-III-450 systems on many of our 3D gaming tests. This speed is probably due to the PC's Diamond Multimedia Monster Fusion graphics subsystem. But the Monster Fusion has some drawbacks that prevent us from recommending this Micro Express as a gaming system. Among the board's shortcomings is the inability to render 3D images in 32-bit color, so some games won't look as lifelike as they might.

Desktop Derby

If your main concern is business, K6-III systems can offer a phenomenal deal, depending on the vendor. They may cost hundreds of dollars less than similarly outfitted PIIIs that run at pretty close to the same speed.

The two Micro Express systems were the fastest in their respective clock-speed and price classes. Their spacious hard drives and large displays are impressive, considering that the systems cost only $1799 (for the K6-3/400) and $2049 (for the K6-3/450). But these are basic machines, without the software bundles or high-quality speakers some of the other systems provide. Micro Express charges $2124 for a comparably equipped Pentium III-450--$325 more than for the K6-III-400, which should run business applications at approximately the same speed.

Compaq's Presario 5600s-450 offers lots of goodies, including a Zip drive and an excellent flat, 15-inch LCD screen. As a result, the Presario costs a whopping $2480. That's still about $600 less than Compaq charges for a similarly configured PIII-500.

The CyberMax Enthusiast KIII-400 costs $1599, and the 450 will run you $1749. Both systems offer something the others don't: a 4.8X DVD-ROM drive. What's more, the CyberMax systems come with good-sounding speakers and a nice selection of software, including WordPerfect Office Suite and several Compton's reference titles. The vendor charges $250 to $300 more for identically configured Pentium III systems.

Leave It at Home

AMD's other new chip, the K6-2 mobile, doesn't match the K6-III's success with business apps. With its top speed of 333 MHz and 3DNow capabilities, this K6-to-go should offer an inexpensive way to take multimedia on the road.

Judging from the one notebook we tested, the chip might just as well have stayed at home. With a PC WorldBench score of only 131, Toshiba's $1899 Satellite 2545XCDT performed more like a Pentium II-233 notebook than like anything with "333" in its name. Why the sluggish performance? One possibility is the lack of an integrated L2 cache, the speed booster that's built into mobile Pentium IIs and Celerons.

Toshiba didn't quibble with our test results, acknowledging that in this case it had traded speed for features--the notebook includes a 14.1-inch screen. The company's Satellite 4030CDT, which costs $100 more, has a much faster processor--a Celeron-300--but its screen measures only 13 inches. Another plus: In PC World's tests of battery life, the 2545XCDT lasted an impressive 3.5 hours.

As always, it's hard to evaluate a CPU based on a single computer, and at press time, Compaq had announced a notebook based on a new 380-MHz K6-2 chip. But if the Satellite 2545XCDT we tested is any indication of what the new chip can do, don't hold your breath.

Would You Bet on AMD?

AMD-equipped PCs have traditionally been sold primarily to consumers, while businesses keep their distance. As analyst Nathan Brookwood of the research firm Insight 64 points out, "People who spend their own money on a computer are more likely to go with AMD. People who spend other people's money will be more cautious."

It's possible that the K6-III will change that. With its relatively low price and its excellent performance on standard business applications, its appeal may spread from home to small businesses, and then to bigger companies, especially if AMD can keep the K6-III significantly cheaper than Intel's PIII processor. Already, every major vendor except Dell and Micron is either selling or planning to sell at least one AMD model.

AMD could gather still more momentum when it introduces its K7 chip, which is expected to appear sometime during the second half of the year. With completely new architecture, 0.25-micron technology, a 128KB L1 cache, and additional improvements, the K7 chip could pose a real challenge to Intel.

This rosy picture has a few thorns. AMD has a history of manufacturing delays with new chips. Last year, for instance, a production line problem kept the then-new K6-2 from coming out as soon as expected. If such a delay happens with the K6-III, you may have trouble getting one of the new chips no matter how desperately you want it, and AMD could become the victim of its own success.

AMD could face additional problems if Intel decides to slash its prices. Clearly, the industry's largest chip manufacturer is better equipped to fight a protracted price war.

What to Buy Now

If you want a blindingly fast machine to run your business applications, you can't do better than a K6-III-450 system. For less than the cost of a Pentium III-450 PC, you'll get the performance of a Pentium III-500. Of course, if all you're running are business applications, you probably don't really need that much power to begin with, and a Celeron-400 or -433 will do just fine.

And if you're addicted to computer gaming, or otherwise need fast and wonderful 3D graphics, you may want to shell out the big bucks for a Pentium III system.