Now I regret buying a single RAM card

[viper37]

It is true that IIRC once the de- and re-plugging of the HDD solved the booting issue I didn't try putting just the old supposedly faulty RAM back, I'll try if I can gather the willpower, thanks.

However, this Intel article would suggest that my mobo (asus z-170 pro gaming) should be able to handle 2 modules in dual channel mode and a 3rd in single channel:
https://www.intel.com/content/www/us/en/support/boards-and-kits/000005657.html#flex

might be a bios issue.  do you have the latest one?

[Tamas]

Heh, so far at least, it does work just with the old 8GB module. I'll see if it ends up freezing again but I wonder what was the original problem then? Well, I have already archived the most important files from the HDD in case that's the one that's dying.

[Tamas]

Ok so I have managed to make the 3 module setup work. The duals are in B1 and B2 as recommended by the manual. This time, I put the lonely 8GB one to A1 - that's a bit harder to access due to the CPU than A2 that's why I was hoping A2 would work but it didn't.

Anyways, now I have BIOS manual-set to 2400Mhz RAM setting to match the slower two of the trio, and it seems to be working. CPU-Z telling me I have 16 gigs of RAM with frequency of 1205 which AFAIK matches as its supposed to be half of the frequency shown per CPU tick.

I'll test it and sleep on what to do, maybe I can return the new 4GB sticks and get a pair for the lone 8GB one, or just keep them AND buy the pair for the 8GB one.

[DGuller]

I wouldn't buy a pair for a 8 GB one.  Unless you have the exact same make and model, they would still be mismatched in some way, and that's always a potential PITA.

[Tamas]

I wouldn't buy a pair for a 8 GB one.  Unless you have the exact same make and model, they would still be mismatched in some way, and that's always a potential PITA.

I meant buying the exact same kind, obviously. But so far I saw no issue with the 3 card setup. Seems to be still applying dual mode to the 2*4gb pair as suggested by the Intel document above, so if there won't be any freezes I'll be fine this way I think.