You know, buying RAM for your computer isn't so easy. There's a lot to take into account: how much to get, what speed you want, and whether it's worth paying a few bucks more to make the inside of your computer look like it's been slathered in rainbow sherbet.
But one specification people don't talk too much about is how many ranks your RAM modules have, and I'm not referring to how many Steam achievements you've unlocked with the same RAM kit. If only.
A memory rank is actually a single group of memory blocks. 
You see, each rank has a 64-bit bus that connects your RAM to your motherboard, and one stick of RAM can have one, two, or even four ranks on that one stick. Generally speaking, more ranks are better because your system's memory controller can access rank separately from the others.
While the CPU can't access every rank at once, due to the modules themselves sharing the 64-bit bus, it can start an operation on one rank while another rank finishes up on another task, a process called interleaving that can reduce memory response time and slightly improve bandwidth despite not increasing the bus width. 
But should you care about this? Are the performance benefits actually worth worrying about such an esoteric topic?
It turns out the answer is yes, especially if you're running an AMD Ryzen CPU. Certain games that are more memory-dependent can see noticeable performance increases when running more ranks of memory, and even some productivity applications, like file compression programs, can also benefit. And there's more good news.
You don't necessarily have to go out and buy special dual-rank modules to take advantage of the speed boost. Many of you probably have four DIMM slots on your motherboard that can operate in dual-channel mode. If you fill all four slots with single-rank DIMMs, this is roughly equivalent to a dual-rank setup in two slots. If you're only rocking two sticks of RAM, this is a situation in which you'll want to have those dual-rank modules.
But how, exactly, do you know how many ranks are on your RAM modules? Ask them? Although a common explanation is that single-rank memory has chips on only one side while a dual-rank module has memory chips on both sides, it can be hard to tell how many ranks a stick of RAM has just by glancing at it, even if it doesn't have a head spreader.
Sometimes modules that appear to have memory chips on both sides actually act as one big rank, and then you have the fact that trying to figure this out in your BIOS or in a system utility doesn't always give you an accurate answer either.
Some RAM modules will have a 1R or 2R to indicate whether they're single- or dual-rank, respectively. 
And quad-rank memory is quite unusual on regular desktops, so odds are you won't be seeing too much of it. If that isn't too helpful, you might try looking at a spec sheet or checking out online resources where users have compiled lists of single- and dual-rank memory kits.
Now, it also turns out that because modern memory integrated circuits, or ICs, tend to be 8-gigabit capacity as opposed to the older standard of 4, newer 8-gigabyte sticks tend to be single rank while newer 16-gig sticks tend to be dual-rank. And if you're confused about the math there, one rank is made up of eight ICs. This means that even if you won't use all of it, 32 gigabytes of memory may be the sweet spot for speed today, though this will keep changing as IC capacity increases.
But remember that whether you see real benefits really depends on your workload, and more ranks can paradoxically add more latency, depending on what you're doing. So do your research and see if that trade-off is worth it for whatever it is you get up to on your PC.
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