MEMORY SPEED TESTS:
iMac Core 7 versus Mac Pro
Posted Friday, December 11th, 2009, by rob-ART morgan, mad scientist
We set out to show how the amount of memory in the new quad-core iMac (Core i7) affects performance. Only two of our tests showed interesting differences. While we keep working on this issue, we want to share with you what we learned so far.
GRAPH LEGEND
MP 12G*8 = 8-core 'early 2009' Mac Pro 2.93GHz with 12GB of RAM (6 x 2G)
with apps run using only 8 cores
MP 12G*4 = 8-core 'early 2009' Mac Pro 2.93GHz with 12GB of RAM (6 x 2G)
with apps run using only 4 cores
i7 16G = 4-core 'late 2009' iMac 2.8GHz Core i7 with 16GB of RAM (4 x 4G)
i7 12G = 4-core 'late 2009' iMac 2.8GHz Core i7 with 12GB of RAM (2 x 2G, 2 x 4G)
i7 8G = 4-core 'late 2009' iMac 2.8GHz Core i7 with 8GB of RAM (4 x 2G)
i7 4G = 4-core 'late 2009' iMac 2.8GHz Core i7 with 8GB of RAM (2 x 2G)
RED BAR means FASTEST
DigLloydTools 2.0 -- Memory Stress Test: This benchmarking tool (which I will call DLT) is run from Terminal. We set the options to gobble up all real memory but not do any virtual memory paging. The numbers below are the results using the 'memcpy' function. To compute total throughput rate, you must double the number (since it is both reading and writing). In the case of the Mac Pro, to make it a fair fight, we forced it to use only 4 and 8 cores though it is capable of using 16 with hyperthreading.
After Effects CS4 -- Using the TotalBenchmark project, we timed the rendering of phase 2 using various multiprocessing options and various memory configurations. In the case of the Mac Pro, to make it a fair fight, we forced it to use only 4 and 8 cores though it is capable of using 16 with hyperthreading.
SOME SURPRISES
First, the Nehalem Mac Pro's memory throughput (measured with DLT's memory stress test) was 150% faster than the iMac Core i7 even though both have memory rated at 1066MHz. One explanation may be the Processor Interconnet Speed. The Mac Pro is 6.4GT/s while the iMac Core i7 is 4.8GT/s.
Second, the iMac Core i7 with 4G of RAM (2 x 2G) had faster throughput that any other iMac Core i7 config. We're not sure why. The config with mixed sizes (12G) ran the slowest. Don't get obsessed with matching memory, though. We have yet to find a real world app that uses the full memory bandwidth.
Third, when running After Effects, the Mac Pro was signficantly faster than the iMac Core i7 even when we "hamstrung" it to use only 4 and 8 cores. (Processor Interconnect again?)
As for the iMac Core i7 with 4G of RAM, it ran After Effects slower than the iMac with more memory because it was only "allowed" by AE to use 4 cores while the others had enough memory to use 8 cores with hyperthreading. I recommend configuring your iMac Core i7 with at least 8GB of RAM if you are running pro apps.
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