64 GB RAM installed but only 32 GB Usable

I have an MSI B450 Tomahawk Motherboard and 2 sticks of RAM, 32GB each Corsair Vengeance LPX 3200MHZ (2x 32GB). The sticks are in slots 2 and 4.

The operating system is Windows 10 Pro (64 bit).

Windows sees the full 64 GB, but shows only 32 GB as usable.

Usable Memory Screenshot

Any ideas? Thank you.

Solution 1:

Your memory modules, part number(s) CMK64GX4M4B3200C16 appear on the QVL provided for your motherboard, and is marked as compatible with your current processor.

However, the maximum speed you'll get with the kit (as per SPD defaults) will be 2133MHz.

To gain access to faster 2933MHz in single rank mode and 2400Mhz in dual rank mode if 2 out of 4 DRAM slots are populated, as referenced in this article by Puget Systems, enable A-XMP, and select XMP Profile 2 in your BIOS settings.

You may want to move the RAM sticks around, as recommended by @Silbee in the comments below, ie to slots DIMMA2 (Slot 2) and DIMMB2 (Slot 4) to enable dual channel memory mode.