Nehalem 4-core versus 8-core:
What's the Real World Difference?
Posted Tuesday, April 3rd, 2009, by rob-ART morgan, mad scientist
You've seen the Cinebench and Geekbench on various websites for both 4-core and 8-core Nehalem Mac Pros but what about real world applications? The 4-core is much more affordable but are there significant performance gotchas that could make you regret not going for the 8-core? After some testing of both the 4-core and 8-core 2.93GHz Mac Pro (both with 12GB of RAM and the Radeon HD 4870), we have a few bare facts to share.
HOW BIG IS THE PERFORMANCE GAP?
|DLT memory stress test
LET US EXPLAIN
DLT memory stress test - The DigLloyd Tools memory stress test uses memmove to transfer memory to and from the CPU. We've talked about triple channel memory in the Nehalem in a previous article. In reality, the 8-core has 6 channels (using 6 slots) and the 4-core has 3 channels (using 3 slots). We equipped the 8-core with 6x2G = 12G and the 4-core with 3x4G = 12G.
Yes, 4GB DIMMs work in the 4-core. We've tested both OWC and TransIntl 4GB DIMMs. They run fast, cool, and stable.
Now don't get too carried away with the memory transfer speed benchmark result. The truth is that most applications do NOT saturate the memory bus. As you can see from the rest of the apps we ran, none of them went 72% faster.
After Effects - We rendered the Total Benchmark project with Multiprocessing enabled in the Preferences. It spawns a subprocess for each core. With HyperThreading enabled, it spawns processes for total physical cores x 2. Each process can gobble up to 3GB of real memory. (Advantage: 8-core by 44%)
Compressor - When we encoded an HD DVD with Compressor 3, we tried various flavors of QuickClusters in the QMaster using from 2 to 8 instances (aka cores). Comparing the fastest times, the 8-core's "sweet spot" was 6 instances and the 4-core's was 4 instances. Once the number of instances was "tuned," the 8-core completed the task 29% faster than the 4-core.
Motion - We did a RAM Preview - Play Range with the Blocks-Detail.HD template. The 8-core created the RAM Preview 7.5% faster than the 4-core.
OpenGL 2.1 - We ran the OpenGL Extensions Viewer benchmark at 1920x1200 with 8X Anisotropy and 4X Multisampling with Fog and Transparency enabled. The table above shows the frames per second attained by the OpenGL 2.1 test. The 8-core was 8% faster.
WoW - We ran our Narache Village warrior tree run at 2560x1600 with all setting maxed in World of Warcraft. The 8-core was 5% faster.
X-Plane - At 1920x1200 with 2X Multisampling and 4X Anisotropy, the 8-core was 4% faster. We ran other games but the 8-core advantage ranged from 0% to 2% -- which we consider inconsequential.
NOT EVERYTHING IS FASTER ON THE 8-CORE
We found two apps that actually tested faster on the 4-core.
Photoshop CS4 - When we ran the performance action file (diglloydSpeed1) designed to simulate a typical photograph editing session, it ran consistently 4% faster on the 4-core.
iTunes - We converted 14 MP3 Beach Boys tunes to AAC. The 4-core was 4% faster than the 8-core.
Is the 8-core's price justified? It depends on the apps you run. It won't be twice as fast as the 4-core running any real world app, that's for sure.
We, like you, are frustrated by the fact that the 4-core only comes with 4 memory slots. Thankfully, Other World Computing and Trans International offer 4GB modules that can take you up to 16GB. Let me say it loud and clear: 4GB DIMMs work just fine in the 4-core and 8-core Nehalem Mac Pro.
We haven't tried all the memory permutations on the 8-core and 4-core yet. OWC informed us that you cannot mix the 4GB DIMMs with other size DIMMs. We were able to mix the sizes of 4G TransIntl DIMMs with 2G DIMMs on the 8-core but the memory transfer speed dropped from 9.5GB/s to 7.5GB/s.
WHERE TO BUY APPLE PRODUCTS
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The Radeon HD 4870 kit can be found on the Apple online store by doing a keyword search such as "4870 graphics." Ditto for the GeForce 8800 GT kit and 120 GT kit.