First, here’s some background. PCs and Macs are either single-core or multicore, depending on the number of processors they house. We don’t refer to software as "multicore" or "multiprocessor," but rather "multithreaded," which refers to an application’s ability to split work among different processors. A nonmultithreaded application can’t split up the processing load, and thus runs at about the same speed on a one-core or eight-core system. My tests revealed that there are "levels" of multithreading efficiency. That is, some programs, most notably Autodesk’s 3ds Max, are nearly twice as efficient with eight cores as they are with four. Alas, both Sony Vegas 8 and Adobe Premiere Pro CS3 seemed more efficient running on four cores than eight, as you’ll see in a moment.
I tested three systems, all from HP. The first was a dual-core Core 2 Duo-based 8710p notebook running at 2.2GHz. The next was a quad-core xw4600 Workstation based on the QX6850-core 2 Extreme Processor quad-core running at 3GHz. The third was an eight-core xw8400 workstation running dual processor, Quad-Core Xeon X5355s at 2.66 GHz. The desktops were running Windows XP, while the notebook used Windows Vista.
I would have preferred two, four, and eight cores with identical speeds, but to normalize the results, I multiplied the number of cores by the processor speed, which gave me relative scores to assess application performance. For example, the notebook had two cores running at 2.2GHz, or 4.4GHz total processing speed. In contrast, the xw4600 had four cores running at 3GHz, or 12GHz total speed, roughly 2.72 times more clock speed than the notebook.
Accordingly, if an application rendered 2.72 times faster on the xw4600 than on the notebook, it took full advantage of the multiple cores and the additional speed.
Interestingly, working with my standard 3.5-minute HDV test project on the xw4600, Sony Vegas produced SD MPEG-2 files in 3:27 (min:sec) compared to 9:02 for the 8710p notebook, or 2.62 times faster, coming very close to the 2.72 theoretical max. Also on the xw4600, Vegas produced an MPEG-4 file from the same project in 6:11, compared to 18:07 for the notebook, which is 2.93X, even faster than the expected 2.72. On the xw4600, Premiere Pro produced a 1440x1080i Blu-ray-compatible MPEG-2 file from the same 3.5-minute test project in 8:47, compared to 23:30 for the 8710p, about 2.68 times faster, again close to the 2.72 differential. Clearly, when jumping from two to four cores, both Vegas and Premiere Pro were very efficient in their multithreading.
Here’s where things started to break down. Using the same type of mathematical comparison, the eight-core xw8400 has 21.28 GHz of total processing speed, 4.8 times that of the 8710p and approximately 80% faster than the four-core xw4600. In the Vegas tests, however, the xw8400 performed more slowly than the xw4600. With Premiere Pro, the eight-core xw8400 proved 20 seconds faster than the xw4600 when producing the Blu-ray-compatible file (8:27 compared to 8:47), an advantage of 4%. This doesn’t seem worth the $1,700 differential between the four-core and eight-core systems. I also tested Encore and produced a 2-minute Blu-ray disc image on both computers. The eight-core system was actually 6% slower.
A quick glance at the processor utilization graphs in Windows Task Manager on all three systems tells the story. You can open Task Manager via the three-finger salute (Ctrl-Alt-Del) and then click the Performance tab, if you’re running Windows XP. Vista adds an extra step in the middle—you’ll need to select Task Manager to get to the screen with the Performance tab. On the two-core 8710p, Vegas used nearly 100% of both of its processors during rendering. On the four-core xw4600, the number averaged around 97%; on the eight-core xw8400, the number dropped to 44%. Adobe numbers were similar, though less well-defined. Neither program used eight cores nearly as efficiently as four, producing similar or even slower results on the theoretically faster system.
At this juncture, more is not better when it comes to cores, at least once you go beyond four. But, as they say in baseball, speed never has an off day. If you’re currently running a two-core system, you can definitely get a real jump in encoding performance by buying a four-core system, and the new generation of quad-core Core 2 Duo processors look like real winners for the editing community.
But if you’re faced with the decision between a moderatespeed eight-core system and a top-speed four-core system, go with the four-core system every time—at least for Vegas and Adobe Production Premium.
Jan Ozer is a contributing editor to EventDV and Streaming Media.