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Memory: It’s Great to Have 64GB in the iMac 5K

See also: iMac 5K (Late 2015) with 64GB: the Key to Professional Usage and New Apple iMac 5K 27" Supports 64GB Memory, OWC Has Kits Available and

Sometimes 16 or 32 GiB memory just won’t serve.

The 64GB OWC memory kit in my late 2015 iMac 5K* took minutes to install and has worked flawlessly.

Shown below is a very busy iMac 5K, chewing up all the CPU cores:

  • 28.3 GiB memory in use
  • 35.6 GiB memory used for file system caching
  • 5 GiB wired (locked down) memory
  • Outstanding: no swap (disk I/O) is being used because of a memory shortage (good!).
  • Compressed memory is only 2.1MB (effectively zero, in context).

Things would slow to a crawl trying to do this on a system with 16GB, and performance would be substantially impaired on a system with 32GB: only 64GB will do for this kind of usage.

* For the first time ever I (Lloyd) bought and am actively using an iMac 5K. In many respects it is superior to the fastest 2013 Mac Pro (3.3 GHz 8-core). Its main weakness is a single Thunderbolt bus with only two ports, a real headache for multiple displays and networking and storage all together (daisy chaining and one bus have real practical limits). So I use it as a compute station for multi-minute Photoshop jobs using wonderfully fast Thunderbolt networking to connect to the Mac Pro.

While 64GB is a smart move for a “set and forget” system for the high-end configuration, many users do not need a full 64GB. So add to the memory already paid for that came with the iMac: Apple configures an 8GB iMac 5K as 2 X 4GB and a 16GB iMac 5K as 2 X 8GB, thus leaving two memory slots open. When a full 64GB is not needed, keep the two modules already there, but add 2 X 8GB or 2 X 16GB as follows:

2 X 4GB + OWC 2 X 8GB ===> 24GB
2 X 4GB + OWC 2 X 16GB ===> 40GB
2 X 8GB + OWC 2 X 8GB ===> 32GB
2 X 8GB + OWC 2 X 16GB ===> 48GB

The iMac 5K uses dual channel memory, so this 2 module + 2 module approach poses no performance issue.

Intensive CPU and memory usage on late 2015 iMac 5K with 64GB OWC memory
64GB OWC memory in late 2015 iMac 5K
Photoshop performance prefs with 64GB memory

See also on the new iMac 5K:

OWC Accelsior 4M2 PCIe SSD
6000 MB/sec!
Mac or PC.

Ideal for Lightroom, Photoshop, video.
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