Mac: 2019 Mac Pro:  Memory Configurations

Created on: December 18, 2019
Last updated: April 19, 2022

Relevant Module Types / Base Modules:

• 'R DIMMS'
  • OWC2933D4MP64G
  • OWC2933D4MP32GB
  • OWC2933D4MP16GB
  • OWC2933D4MP8GB
  • OWC2666D4MPE32G
  • OWC2666D4MPE8GB

• 'LR DIMMS'
  • OWC2933D4LR128G
  • OWC2933D4LR64GB
  • OWC2666D4LRE64G

Apple has provided an excellent resource for understanding the best way to pair modules in the 2019 Mac Pro, including mixed capacity pairs, and troubleshooting with 1, 2, or 3 modules. Please review their support page carefully before installing new RAM modules, specifically: 

Supported Configurations

Mixed Capacities

and

Verify Memory

Some key takeaways from OWC: 

• Do not attempt to mix and match 'R DIMMs' with 'LR DIMMs'; this is not supported. If attempted the computer will not boot and the related LEDs will blink orange.

• From the list above 'R DIMMs' can be mixed and matched in pairs, or with Apple's (8GB, 16GB, or 32GB)  'R DIMMs' 
  
• When using 'LR' DIMMS you need to use at least 4 modules at a time or else the system will generate an error message.
• When using 'LR' DIMMs listed above, you cannot have multiple capacities of this type of module, installed at the same time.
  • Examples:
  • You cannot have pairs of both OWC2933D4LR128G and OWC2933D4LR64GB installed or
  • OWC2933D4LR128G and OWC2666D4LRE64G or
  • OWC2666D4LRE64G and OWC2933D4LR64GB
    
    
• When 128GB or more are installed, you may notice after booting the Mac Pro, the screen will remain blank while the OS loads and then immediately display the Desktop (i.e. no progress meter or Apple logo).
  • Similarly, when more than 128GB of RAM is installed, the Apple Diagnostics screen may remain blank for 4-5 minutes as it loads.
    
    
• Modules should be added in pairs and the capacity of the pairs will determine which slots should be used for which modules (see links above).
  • Configurations for 1, 2, or 3 modules are only for troubleshooting and each setup requires that a specific slot(s) be used.
    
    
• Sometimes when you seat the modules and press them into place, the locking tabs on either side of the module may not fully snap into place. A bit of additional force is required near the corner of the module where the tab is "stuck" to pop the tab into place. If modest additional force does not work, do not force the module! Instead remove the module, re-align with the slot, re-seat then try again to snap it into place.