[SOLVED] 16Gb of RAM but only 7.95Gb Usable (sometimes)

[LegsaB]

I bought a new 8Gb stick of RAM for my PC and it's pretty weird how the whole 16Gb is usable when i open BIOS when starting my computer and change the memory Try it! mode and exit the BIOS. PC then fails to start for 3-5 times and then works fine and all of the RAM is usable. If i dont open BIOS when starting maybe 1/10 times all of the RAM is usable.
The stick are different label but same speed etc.
Crucial 8GB Ballistix Tactical, DDR4 2666MHz, CL16, 1.2V
Corsair 8GB (1x8GB) Vengeance LPX, DDR4 2666MHz, CL16, 1,2

 

[popatim]

Specs don't mean a lot when your talking about disparate memory stick working together. The recommendation is to buy a dual channel kit to ensure they work together. Anything else and you might as well flip a coin.
Try going into the bios and setting the ram back down to the slowest stock speed you see. See if it works reliably. If so then go back in and raise it up a notch and retest. repeat until you find the highest you can go. before you get issues.

 

[alceryes]

Memory should only be used together when it is sold in one kit. These are different sticks of RAM and are not guaranteed to work together.
Also, the 'Try It!' button is a timing overclock. So you already figured out they won't work together in overclock mode. You should first see if they are stable together at 2666MHz (no Try It!). Boot from a memtest86 USB and let it run through at least one PASS.