Original post by: Ian Brandt ,
According to Apple my early 2011 MacBook Pro [http://support.apple.com/kb/sp620|only supports up to 8GB]. I've been happily running it with 16GB for years now without issue. That said according to Intel's [http://ark.intel.com/products/80810/Intel-Core-i5-4690-Processor-6M-Cache-up-to-3_90-GHz|i5-4690] and [http://ark.intel.com/products/80807/Intel-Core-i7-4790K-Processor-8M-Cache-up-to-4_40-GHz|i7-4790K] specs the maximum supported memory is 32GB. More details [http://www.intel.com/content/www/us/en/processors/core/4th-gen-core-family-desktop-vol-1-datasheet.html|in the datasheet]: "Using 4Gb DRAM device technologies, the largest system memory capacity possible is 32 GB, assuming Dual Channel Mode with four x8 dual ranked DIMM memory configuration". See also an [http://www.intelligentmemory.com/faq/end-customer-faqs/on-which-intel-cpu-based-systems-will-the-intelligent-memory-16gb-unbuffered-dimms-and-so-dimms-work.php|Intelligent Memory FAQ entry on the issue]. While I'd be happy to see someone get their hands on some [http://www.anandtech.com/show/7742/im-intelligent-memory-to-release-16gb-unregistered-ddr3-modules|16GB SO-DIMMs] and prove otherwise, my limited guess is that 64GB support in the Late 2014 iMac is unlikely. As for why anyone would need or want 64GB RAM in a desktop, any sort of analytics over about-that-size datasets is the first thing that comes to mind. Perhaps also developing and testing in-memory databases, or cluster technologies with bunches of VMs. The 1TB PCIe SSD is quick, but RAM is still a lot faster. Smoke 'em if you got 'em.