32 GB RAM (16 GB usable) at wits end

[positivecharacters]

I am at my wits end trying to figure out why only 16 GB of RAM is usable out of 32 GB installed. I believe initially when I purchased both the motherboard and RAM all 32 GB was available. It also only shows my RAM as being single as opposed to double. From what I understand the actual memory is not SINGLE or DOUBLE. All four modules are the same make, model, and size. I have rearranged the four modules and made sure they are securely installed. I thought purchasing new RAM would solve the problem. I checked my BIOS and I am not able to make any changes. Please help!

Motherboard:
GIGABYTE GA-990FXA-UD3 R5 (rev. 1.0) AM3+/AM3 AMD 990FX SATA 6Gb/s USB 3.0 ATX AMD Motherboard
Intial RAM:
Corsair Vengeance Pro Series 16GB (2x8GB) DDR3 1866 MHZ (PC3 15000) Desktop Memory
New RAM:
Corsair CMZ8GX3M1A1600C10 Vengeance 8GB (1x8GB) DDR3 1600 MHz (PC3 12800) Desktop Memory 1.5V

 

[CrazyDingo]

The ram's not guaranteed to work unless you buy it as a kit - if you want 32 GB, you need to buy a 32 GB kit.

 

[geofelt]

Your new ram says 1600 speed, the original says 1866.
A motherboard must manage all ram at the same speed, voltage and cas.
If you got it to work, it all would run at 1600.

Yes, ram must be installed in a single matched kits to be compatible.
The internal workings are designed for the capacity of the kit.
Ram from the same vendor and part number can be made up of differing manufacturing components over time.
Some motherboards, can be very sensitive to this.
AMD, in particular is very sensitive to ram.
This is more difficult when more sticks are involved.
That is why ram vendors will NOT support ram that is not bought in one kit.

To get things to work, the only suggestion I can make is to get into the bios and try increasing the ram voltage.
Sometimes that works.

Test the ram with memtest86.
You should be able to complete a full pass with NO errors.

Lastly, the FX line is old and close to obsolete.
I would not spend any more on it.
Sell your parts and look for a modern ryzen or 8/9th gen intel based build.

 

[positivecharacters]

Your new ram says 1600 speed, the original says 1866.
A motherboard must manage all ram at the same speed, voltage and cas.
If you got it to work, it all would run at 1600.

Yes, ram must be installed in a single matched kits to be compatible.
The internal workings are designed for the capacity of the kit.
Ram from the same vendor and part number can be made up of differing manufacturing components over time.
Some motherboards, can be very sensitive to this.
AMD, in particular is very sensitive to ram.
This is more difficult when more sticks are involved.
That is why ram vendors will NOT support ram that is not bought in one kit.

To get things to work, the only suggestion I can make is to get into the bios and try increasing the ram voltage.
Sometimes that works.

Test the ram with memtest86.
You should be able to complete a full pass with NO errors.

Lastly, the FX line is old and close to obsolete.
I would not spend any more on it.
Sell your parts and look for a modern ryzen or 8/9th gen intel based build.

Thanks for the info. I had 4x8 of the 1866 all same make, model, capacity. THEN I changed to 4x8 of the 1600 same make, model, capacity. However, I have taken your advice and plan to build a new computer with new components and order a complete 64GB DDR4 ram set when I do (i'm upgrading the mobo, psu, processor, and case.