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2019 iMac 5K: Memory Bandwidth
Related: 2019 iMac 5K, 4K and 5K display, bandwidth, iMac, iMac 5K, Macs, memory, memory bandwidth, video
MPG tested the 2019 iMac 5K 3.6 GHz Intel Core i9 8-core / 128GB / 2TB / Radeon Vega 48. Purchase with 8GB memory, then add 64GB or 128GB OWC memory. See recommended Macs for photographers and videographers.
These tests made possible by loaner gear from B&H Photo and OWC, so please buy your gear at B&H Photo and OWC/MacSales.com using any link from this site or MacPerformanceGuide.com, ditto for OWC/MacSales.com. See also 2019 iMac 5K: Recommended Models and Accessories.
Unsure which Mac to get or how to configure it? Consult with Lloyd.
But the iMac 5K with 8GB, then upgrade the memory to save about 50%.
There are two different 64GB memory kits from OWC for the 2019 iMac 5K: a 2-module kit and a 4-module kit (less expensive). The 2-module kit costs more because it uses higher-density memory chips, which are more expensive. If going with 64GB, MPG recommends the higher-priced 2-module 64GB kit (2 X 32GB) if there is any potential for later needing 96GB or 128GB*.
* Since the 2019 iMac 5K uses dual channel memory, four modules versus two has no bearing on memory bandwidth, unlike the iMac Pro.
This page uses the mt stress command of diglloydTools MemoryTester to evaluate memory bandwidth with a real application using all CPU cores. Not to be confused with memory or CPU specifications—this is the real deal, whatever bandwidth an application actually has available to it combined with what any operating system overhead entails.
Memory bandwidth is especially important for more CPUs and/or fast ones. All iMac 5K Macs through 2019 offer less than half the memory bandwidth of the iMac Pro. But only geeks focus on that—what matters is actual performance as the sum of all capabilities.
The 2019 iMac 5K shows the same memory bandwidth (within measurement error) to the 2017 iMac 5K. Possibly having twice the cores introduces enough overhead to show this 0.7% difference and/or macOS 10.14.4 vs macOS 10.13.6 and/or background processes. The difference is below measurement error = no difference.
Tested with 128GB OWC memory.