P55C). The Windows version of the new Photoshop takes advantage of the P55C's MMX architecture.
As noted p
reviously in BYTE (see "x86 Enters the Multimedia Era," July 1996), the P55C has 57 new instructions to accelerate MMX-optimized applications' video, graphics, animation, and sound performance. However, the processor also provides 16 KB each for the primary instruction and data caches, double that of previous Pentiums. Intel reckons that even current applications not optimized for MMX will see performance boosts of 10 percent to 20 percent. Applications optimized for MMX should see even better improvement than that, depending on how aggressively they have been tuned. Except for applications optimized for MMX, today's Pentium Pro is still the performance champ for 32-bit or floating-point-intensive applications.
Many multimedia and games developers are optimizing for MMX, as are Adobe competitors, such as Corel. BYTE saw impressive improvements in MMX-optimized 3-D applications and games, but, unlike Photoshop 4.0, those applications were in prerelease stage.
Photoshop has long had what Adobe calls a "
bottleneck architecture," in which compute-intensive operations are isolated. This approach allows developers of hardware accelerators or multiprocessing systems to write custom code to accelerate time-consuming processes. Adobe's claims that performance might jump two to six times with MMX processors made us wonder if Pentiums with MMX technology will outperform a high-end Macintosh. Photoshop is often run on dedicated workstations on a network. Could an MMX Pentium outperform a high-end Macintosh?
The answer: no. Although MMX delivered dramatic performance in some operations (
see the chart
), overall, a high-end Mac still beats an MMX Pentium. BYTE tested three 200-MHz systems from Polywell: a standard Pentium, an MMX Pentium, and a Pentium Pro. In addition, we tested Apple's Power Mac 9500/200 and a Cyrix P166+based PC.
Using a high-resolution RGB image (8.17 MB), we copied the file to every system's local hard drive and installed Photoshop. We repeated each test at least
three times, reverting to the original or undoing the operation each time, using Photoshop's internal timer, and taking the arithmetic mean of the results. The tests are as follows:
Arbitrary Rotate.
Sometimes used for squaring up scans and otherwise used as a special effect, arbitrary rotation uses floating-point calculations, which is why the Pentium Pro beat the P55C in this test. We used 7 degrees clockwise.
Unsharp Mask.
To overcome the loss of apparent sharpness in printed halftones, almost every image that passes through Photoshop has this filter applied. We tested this with two settings: first with the default values (50 percent, radius of 1 pixel, no threshold), and again with more-demanding custom values (50 percent, radius of 10 pixels, threshold of 5). While these values were excessive for the image under test, a radius of several pixels and some threshold will normally be used in production. While most images need more than the default, the default test
is one in which MMX really shines.
Gaussian Blur.
This filter is often used to remove scanner artifacts and to throw distracting backgrounds out of focus. We used the default value of a 3-pixel radius. In this test, the MMX again beat all other systems.
RGB to CMYK.
Normally the last step of every file being prepared for print. For this test, we used the default Photoshop color tables. The MMX chip had an advantage over the existing Pentium architecture, but it still fell behind the Mac.
For most production Photoshop users, the custom Unsharp Mask filter is the most important test. This filter is used regularly. RGB-to-CMYK conversion and Arbitrary Rotate are the next most important tests.
Overall, even without weighting the results to reflect this, the high-end Macintosh system beats the MMX Pentium. But the MMX system ($2996 as tested) delivered slightly better performance than the high-end ($4429 as configured) Mac in two tests. MMX definitely improves the
performance of optimized applications, and at a cost of $550 each (200-MHz version) for PC makers, the first MMX chips cost only $41 more than the current 200-MHz Pentium chip. The jury is still out on other MMX applications. BYTE will test more MMX-optimized applications in upcoming issues, but Photoshop 4.0 portends higher-performing Windows programs to come.
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MMX's performance improvement is greater with some operations than with others. Results are in seconds; lower numbers are better.
MMX: Better in Fits and Starts
