In December, I tried to add some RAM and storage to one of my servers. The storage went well, but the RAM didn't take.

More accurately, the RAM was seen, but it wasn't seen as the whole. On 18 December, I posted that I installed two more 16GB sticks of RAM, but didn't get the 64GB I should have. All four 16GB sticks were recognized, but the system only showed 32GB. I shuffled and rearranged the sticks, but couldn't get any more than 32GB to appear.

I reached out to ASUS support, who directed me to their hardware compatibility tool for the motherboard. On the tool, it showed that the kind of RAM I bought had a "1,2" allowed configuration bit in their list, and they suggested that I needed to find RAM that had a "4" in that spot. I grumbled and resigned to return the RAM, and possibly purchase more. To buy a quad set of memory would require me to discard the 32GB I have in there, and cost more than I wanted to spend, so I decided to wait and maybe build a bigger system later.

Then I forgot to return the RAM. I'm not great at returns, but this kind of sucked because the package has a $99 sticker on it (although I bought it for $59).

I lamented about this here, more than once, and someone reached out and suggested that I might have not had the memory installed in the right slots. Clearly, there are only four slots, so to get all four recognized, they must have been inserted. DDR RAM is installed in pairs, of course, but can sometimes work in single sticks. These DDR4 sticks come in sets with all manner of "must be installed together" markings.  My pal suggested that I might have had one from each pair of my 32GB kits installed in each RAM bank. The four memory slots are split into two bank pairs.

I know all of that, and was pretty sure I'd done that bit right, at least in one of the permutations I'd tried. But I was uncertain.

Today I decided to give it another try. It takes longer to boot the machine than to install or remove the hardware. I shuffled some things around, pulled the case off, and verified the RAM installed. As I expected, the RAM that remains are installed in the two slots for bank A. That should mean that I removed the other two from bank B, of course.

I recalled that I had taken them all out to make sure I had the right pair as I prepared to repackage them for return, so maybe I didn't have them installed that way, but did reinstall the memory in the bank slots as I cleaned up. Curiously, if splitting the RAM into one-each of the separate banks, they will still both be recognized. This, of course, is the "1,2" in the hardware compatibility list; one in each bank, or two in one bank.

I slipped the new sticks in the slots between the installed sticks and made sure everything was nice and snug. I started the machine, but missed the "hit the key for BIOS" moment, so I restarted it and got in there. Low and behold, 64GB of RAM!

I put the case side back on, stood the server back on its feet, and returned to my desk. When it finished booting, I checked again, and the OS sees all 64GB, too!

I must have tried the RAM in six or seven different sets of new first, old first, new only, old only, and so on. But maybe in my hustle I didn't correctly interleave them. Can't imagine I would have missed that, as the banks are clearly marked on the board, and this isn't my first build. Still, I didn't get it right before, so I must have munged that.