Prelim Performance Analysis:
new iMac with Retina 5K display
Posted Tuesday, October 21, 2014 by rob-ART morgan, mad scientist
We are excited about the new iMac with Retina 5K Display. We ordered the 4.0GHz Quad-Core i7 model with Radeon R9 M295X GPU for our long term testing, but plan to benchmark it against the 3.5GHz quad-core i5 with R9 M290X GPU as well as models of non-Retina iMac.
Meanwhile, here's our list of the key performance enhancements:
BETTER SCREEN
The "Best for display" setting of the Retina 5K will be 2560x1440. Using the Displays System Preference panel, you will be able to scale the resolution up or down similarly to how it works with the Retina MacBook Pro. Some apps will offer you the choice of running at the full 5120x2880. Some will not. Whatever resolution you scale it to, the pixels-per-inch (ppi) will remain the same, thereby preserving the 'Retina' effect.
FASTER GPU
To drive the extra pixels, you need a more muscular GPU. Apple has provided the Radeon R9 M290X (2G) and M295X (4G) options.
Keep in mind that this is a mobile GPU. It will not provide the same performance as a desktop R9 290X or R9 295X -- both of which use the "Hawaii" chipset. The iMac mobile version uses the "Tonga/Amethyst" chipset comparable to the desktop version of the R9 275. However, expect the M295X to run OpenGL intensive apps faster than the GTX 780M in the best non-Retina iMac and equal to a single FirePro D700 in the 'late 2013' Mac Pro.
Why AMD instead of NVIDIA? One guess is Apple's emphasis on OpenCL. AMD GPUs tend to beat their NVIDIA counterparts by a large margin in the LuxMark OpenCL benchmark. Needless to say, we will be running our full suite of OpenCL and OpenGL benchmarks comparing the 5K iMac with AMD GPUs to other models of iMac with NVIDIA GPUs.
FASTER CPU
The top Quad-Core i7 is now clocked at 4.0GHz with Turbo Boost up to 4.4GHz. Compare that to the top Quad-Core i7 offered in the non-Retina iMac at 3.5GHz with Turbo Boost up to 3.9GHz.
If you choose the 3.5GHz Quad-Core i5, keep in mind that, though it has Turbo Boost up to 3.9GHz, it does NOT support Hyper-Threading. It will not render with eight virtual cores the same way the Quad-Core i7 does. If your most demanding apps use more than four cores to render, you will want to spend the extra $250 for the Quad-Core i7.
THUNDERBOLT 2.0
What does this mean? It means that if you have external flash storage attached like the LaCie Little Big Disk Thunderbolt 2.0, you will see the full 1348MB/s sequential READ speed (AJA System Test, 16G Test Size). The non-Retina iMac with Thunderbolt 1.0 limits the same storage device to 893MB/s sequential READ speed.
However, if you connect and stripe two LaCie LBD TB2s, you won't see 2609MB/s. Why? Because the two Thunderbolt 2.0 ports share the same bus. Only the 'late 2013' Mac Pro has multiple Thunderbolt 2.0 busses (for six ports) and supports bridging like we demonstrated in our benchmarking of up to three LaCie LBD TB2s.
FAST but not FASTER FLASH DRIVE
UPDATE: Our iMac arrived early. First test we ran was AJA System Test (16G test size). Max READ speed was 816MB/s and average READ speed was 776MB/s. We were hoping for an upgrade to match the 1000+MB/s average READ speed we measured on the 'mid 2014' MacBook Pro and 'late 2013' Mac Pro .
SPEED TEST RESULTS FOR THE IMAC 5K
Go to our INDEX page for a list of several pages featuring the iMac with Retina 5K Display compared to other Macs.
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