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OWC 128GB Memory Kit: Bandwidth
Related: 2013 Mac Pro, bandwidth, Mac Pro, Macs, memory, memory bandwidth, Other World Computing
The OWC 128GB memory kit for the 2013 Mac Pro is manufactured with 1333 MHz parts, but runs at 1066 MHz when installed (this is a technical limitation). By comparison, the 64GB runs at full speed—1866 MHz—a substantial theoretical difference.
On the server-class CPUs (12-core sold by Apple, 8-core 3.3 GHz, 10-core 3.0 GHz), the modules unfortunately run at 800 MHz. But on the stock 4-core, 6-core, 8-core models as shipped by Apple, they run at 1066 MHz.
The difference in memory bandwidth as tested via the system call memcpy()* is substantial, as seen in the graph below, but in real-world applications the CPU on-chip cache largely masks the difference in memory speed; see the tests that follow.
Moreover, when more memory is needed, more memory always trumps memory speed. By the same token, if 64GB is already ample, going to slower-speed 128GB memory is not a win. In short, 128GB is for computing tasks with large data sets, such as huge Phtooshop files, large 3D modeling jobs, databases with large in-memory caches, etc.
Additional notes on the OWC 128GB memory kit
- The OWC 32GB modules (4 X 32GB = 128GB) are manufactured using 1333 MHz parts, but run at 1066 MHz due to technical limitations.
- The 32GB modules can be mixed with 16GB modules, so (for example), a 96GB configuration is possible (2 X 32GB + 2 X 16GB).
- While a single 32GB module should function (mix) with the 16GB modules, OWC advises pairs of matched modules.