UEFI configuration for DDR4 memory on ASRock X99 Extreme3

The RAM counseled for the ASRock X99 Extreme3 by the Crucial website goes only up to DDR4-2666, while the one you bought is DDR4-3000.

The motherboard evidently can adapt itself, as it can manage to work with three RAM sticks, but not with four.

The usual suggestion in such a case is to up the voltage to 1.5v, as higher-powered RAM requires more voltage. However, the motherboard in question can only go up to 1.39, which I believe was not enough in this case, so this is not an option.

The only way to reduce the voltage required by the RAM is to reduce its frequency, which was apparently the solution taken by the workshop that made it work for you with four RAM sticks.

Your options then are either to work with four RAM sticks but with reduced speed, or stay with three RAM sticks working at the full speed of the motherboard (which is still below the true capacity of the RAM your bought).

I payed an IT guy to figure it out and he simply pulled and plugged bars from the 3rd and 4th bench with reboots in between. That, he said approximately, triggers the auto-configuration of quad-channel mode.

The sequence was as I recall, insertion of one in the 3rd bench, reboot, check the recognition in the EFI menu, shutdown, put that one in the 4th bench, then reboot, check, shutdown, put the 4th bar in the 3rd bench. And reboot. And that was it. The 4 bars where recognized and operate with 2400MHz and I have 16GB RAM which was all I ever wanted, except for buying the right modules in the first place.

I did reset the memory settings (timing etc.) before he started. And he checked the bars for marks indicating the order, but there were none.