So when I installed the RAM, all four modules, it only detected 16GB of ram instead of 32GB. When I turned the system off and took all modules out and reseated them, I restarted and it only detected 24GB and there was a red light by slot 1. I took the module from slot 4 and replaced it with the module on slot 1 (keeping the old module that was in slot one out). It detected 24GB of ram which was good, I only had three modules installed.
Finally, when I put the last module back in and started my system, all 32GB of ram was detected. Does anybody know why this happened?
Mac Pro is configured for 1.5 Volt Memory Mac Pro is configured for 1.5 Volt Memory You should be aware that most of the new 16 GB DIMMs are 1.35 V (low-voltage DDR3). The motherboard of the Mac Pro (4,1/5,1) is configured for 1.5 Volt memory. Nevertheless, I suppose Low Voltage memory should work in Mac Pro 4.1/5,1. However, i would prefer 1.5 V DDR3 memory. I quote: DDR3L (low-voltage DDR3) is just an 'extension' of the DDR3 standard, so companies has to be aware that plugging a module will default to 1.5V on most systems. At 1.5V, the worst that will happen will be a waste of electricity/battery.
While the iMac uses high-quality but consumer-grade RAM, the Mac Pro typically uses some of the most expensive RAM available, and the base model currently ships with 12GB of RAM installed.
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RAM modules contain pre-defined configurations (SPD, XMP, etc.) but the default one is often safer value that will work on as many systems as possible. For compatibility purposes, that setting might not be factory-set to 1.35V, but 1.5V instead. The default timings can also be different and slower from the ones indicated on your module package (I have an other answer on this topic). For this reason, there's no chance it will overclock by itself even if it's running at a higher voltage (unless your current BIOS settings are manually set to run at specific speeds higher than your new modules would support - if so, reset your memory settings to AUTO before installing them). If your RAM contains a XMP profile, try that as it can be factory set to 1.35 and all ideal settings - but you still have to select it manually in the BIOS. In conclusion, 1.35V is perfectly safe. It's still always a good idea after installing RAM to go in the BIOS and verify/adjust the settings to ensure they match the module packages and perform optimally.