• PC World
• » Components
• » Processors

The latest Pentium 4 processor not only passes another megahertz milestone by running at 3.06 GHz, it also introduces Intel's new hyperthreading technology to the desktop.

Hyperthreading enables one processor to act like two. As a result, it can simultaneously tackle multiple applications (or a single application that has multiple threads), put idle CPU cycles to use, and boost system performance by up to 25 percent--all without requiring specially written applications, according to Intel.

Sounds good, doesn't it? Exclusive PC World tests on three of the first systems to use the new processor, however, show that hyperthreading's benefits largely are application- or even task-specific. For example, on the office applications that most people use--such as Microsoft's Word and Excel--hyperthreading had a neutral or slightly negative impact. And on tests specifically designed to expose the benefits of hyperthreading, many improvements were too slight to be detectable by the average user, except with select filters in Adobe Photoshop, with various video and photo programs such as Adobe Premiere and Roxio VideoWave, and on certain multitasking tests.

Furthermore, a comparison system equipped with AMD's Athlon XP 2800+, which runs at 2.25 GHz, more than held its own against these 3-GHz powerhouses that were running 800 MHz faster. Nevertheless, hyperthreading remains a very new technology, and Intel anticipates further performance improvements as applications are modified to take better advantage of it.

We tested three shipping 3.06-GHz P4 systems, each packing 1GB of 1.066-GHz RDRAM and running Windows XP Professional. (Currently, hyperthreading works only with either Windows XP Professional or Home, or with such major distributions of Linux as SuSE or Red Hat; these OSs can recognize the technology and use it as they would two physical processors.) Our P4 PCs included the Dell Dimension 8250 ($3419), the Falcon Northwest Mach V ($3288), and the Gateway 700XL ($3899), each loaded with high-end components and ready for the most demanding computing tasks.

Our two shipping comparison machines were Falcon's Athlon XP 2800+ Mach V, carrying 1GB of 333-MHz DDR SDRAM ($2786), and Xi Computer's MTower DPR, with two 2.8-GHz Xeon CPUs and 512MB of 800-MHz RDRAM ($3924). Like the P4 systems, the two comparison PCs ran Windows XP Pro; we tested all Intel-based PCs with hyperthreading both on and off.

Iffy on Office Apps

On our PC WorldBench 4 test suite, hyperthreading produced little positive effect--as we expected given that the multiprocessor-aware OS imposes a performance penalty because it requires additional resources to run (see " Test Center: Notes From the Lab"), and PC WorldBench 4 uses many standard office apps that can't take real advantage of hyperthreading when run singly. The Athlon XP system scored 130, besting all three P4 PCs as well as the dual-Xeon unit. In fact, the score for each P4 system was the same or slightly worse with hyperthreading turned on. The Falcon suffered the biggest drop, from 127 with the feature disabled to 121 with it enabled.

Also, with hyperthreading two of the three 3.06-GHz systems scored 7 to 8 percent lower than the average of five previously tested P4 systems running at 2.53 GHz (121) and of six at 2.8 GHz (123).

Hits and Misses

To better examine hyperthreading technology, the PC World Test Center devised several tests. Our analysts created two using Photoshop, engineered two multitasking tests, and added snippets from the still-in-progress PC WorldBench 5 (due later in 2003).

Our first Photoshop test employed 20 commonly used filters--most of them specified by Adobe and by PC World's art department, with a few chosen from Intel's recommendations. Since Photoshop is a multithreaded application, we expected some improvement with Intel's new technology, but the Athlon XP PC beat the P4 and Xeon systems regardless of hyperthreading status. The Dell PC received a 2-point boost from hyperthreading--the largest among the P4s here, but scarcely noticeable by most users.

In a second round of Photoshop tests, we used 20 filters selected by Intel to showcase its technology. Using these filters, which often incorporate intermediate calculations that hyperthreading can run in parallel, the P4 machines did show marked improvement. For example, the Dimension 8250 completed the test in 118 seconds with hyperthreading turned off (slower than the Athlon XP system's 104 seconds), but reduced its time to 96 seconds with the feature turned on--certainly a significant improvement.

Hand-timed multitasking tests proved a mixed bag for the P4 systems. In one test the photo-management application ACDSee converted 315 TIFF files into JPEGs in the foreground, as McAfee VirusScan checked a directory of folders in the background. Though the P4-based systems all outperformed the Athlon XP PC here, hyperthreading's benefits were far from uniform. For example, the Dell experienced a 4 percent slowdown on ACDSee, but a 4 percent boost on McAfee, whereas the Gateway netted an 8 percent boost on McAfee and no slowdown on ACDSee. In every case, however, running the applications consecutively took less time than running them concurrently.

The opposite was true on a different multitasking test. Here, we used Ahead's Nero Burning ROM to re-create a 490MB hard drive image in the foreground and used Musicmatch to convert ten WAV files into MP3s in the background. Unlike in the previous tests, running the two applications simultaneously was faster than running them separately--by about 30 seconds for the P4s and by 53 seconds for the dual-Xeon PC. Again, the P4-based systems performed best overall, and many performed slightly better with hyperthreading in the concurrent runs.

In testing VideoWave, we used AVI files, DivX-based files, and MPEG-2 files. Scores fell slightly or remained the same with hyperthreading enabled on the AVI and DivX files, but they improved by over 10 percent on the MPEG-2 files.

Bottom Line: Hyperthreading's effects vary widely, and depend on what application--or set of applications--you run. In most cases, however, it seemed to have only a slight effect. And the only way to gauge how your favorite applications will react is to try them out. (See the charts above for all test results.)

Technology a Bust?

Why would a speedier chip that is capable of acting like two processors have so little positive impact on test scores?

"One ill-behaved application could cause problems in a hyperthreading PC," suggests Kevin Krewell, general manager at research firm MicroDesign Resources. That's because while the new P4 tricks the operating system into believing it is two chips, it still has the resources of just one.

For example, the new P4 shares its on-board cache as needed, but it splits its write buffer resources in half--so a single-threaded application that once had access to all eight write buffers can now only use four, he explains.

Brian Fravel, Intel's marketing manager for desktops, claims that with hyperthreading enabled, "The vast majority of applications will be neutral to positive in a stand-alone environment, and almost all applications will see a benefit when multitasking."

The key to taking advantage of hyperthreading is not merely to run multiple programs or a multithreaded application; it is to make sure that those programs hammer the processor with tasks, says Dean McCarron, a principal analyst at Mercury Research. "Both threads need to be throwing instructions at the processor simultaneously," he says.

Though software doesn't need to be optimized in order to use hyperthreading, vendors can tweak their programs to utilize the technology better, says Intel's Fravel. The company won't disclose specifics, but according to Fravel the developers of image- and video-editing applications will probably be among the first to optimize their current offerings. "When you look at video encoding and transcoding today, it's so processor intensive. There are so many places where, if you write it to use hyperthreading, you can take advantage of those unused processor cycles," Fravel says.

Video game programmers could also make multithreaded hay, simultaneously increasing the sophistication of artificial intelligence engines and developing a more realistic 3D environment, he adds.

Intel clearly hopes hyperthreading will make PC sales jump ahead of where they are today, says MDR's Krewell.

"If you look at the timing, Intel is clearly trying to goose the market," he says. "Intel will have the latest and greatest chip with the newest buzzword, and that could be a substantial marketing tool."

Competition Ahead

Don't expect the competition to sit still as Intel trumpets its new technology. AMD will launch an improved version of its current Athlon XP chip, code-named Barton, and its 64-bit Hammer-based processors, sometime in the first half of 2003. According to Krewell, the highly efficient Hammer, which comes with on-board memory controllers, should help AMD compete vigorously against Intel's hyperthreaded Pentium 4.

In the meantime, though, for straight-ahead performance and price, you're likely better off choosing one of Intel's older P4 machines or a high-end Athlon XP-based system. If you are serious about multithreaded applications or you use video or photo editing programs heavily or you multitask as a matter of course, the new P4 systems may suit you. Just remember to choose your applications carefully.

• See more like this:
• 3 GHz,
• 3-GHz,
• Pentium 4,
• P4,
• CPU,
• hyperthreading,
• hyperthread