I am buying a completely new computer around May, and I have a question about RAM kits. My situation is the following: I will eventually need a lot of RAM, but not at the time of the build. I am thinking about buying just one 16 GB stick, and the buy the exact same type of RAM stick every 1-2 months, until I have 64 GB. I plan to use the Z270 platform. My current favorite is the Corsair LPX 16 GB 2400 MHz.
However I heard that it can cause issues especially with XMP. I don't want to overclock the memory, if I can get the 2400 MHz and dual channel, I will be happy.
Can I buy the RAM gradually, or do I need to save a bit more and buy a 4x16 GB kit?
Well a kit basicly means that those particular modules are tested to work together. However that of course does not mean that you couldnt just buy a single stick now, and and expand over time with the same memory modules. I personally dont really see much of an issue with that. Especially not with 2400mhz which should be supported out of the box on Kabylake.
Early Skylake and Haswell-E had some issues with mixing and matching ram kits, but I assume the updated Z270 platform and Kaby Lake will be matured enough to mitigate these issues. I say your probably fine to buy one stick of 16gb at a time without worry.
My rule with buying ram has always been: Buy all the RAM you possibly can, max the board supported RAM or your budget, but remember that in future should you want to upgrade you likely will not find the same matching ram again.(Unless you're willing to do extensive research, find another DIMM with the exact RAM chips on it and then flash the SPD via i2c bus to match the timings.) I just generally discourage mix match ram setups due to stability or performance reasons. Btw if someone wants a tool to flash RAM SPD data via i2c on linux i made a project on github, but it's still in its infancy.
When a friend of mine bought a new PC he needed new (DDR4) RAM and gifted me his old (2x8GiB DDR3) RAM. Luckily, I discovered it was basiacally the same type of RAM as I already had in my PC, so I added these modules to mine and everything worked perfectly. So, I think that as long as everythings the same and it is manufactured by the same company you should be fine.
Just buy the bare minimum you need for now, then get the rest later. DDR4 still has some way to go before reaching maturity. By then, there wont be much need to bin the IC's, so you can mix and match to your hearts content; not to mention, they'll be much cheaper than what they are today ;)
So long as you're buying the exact same spec sticks I see no issue with this. I've run some goofy shit on my z170 for a minute now, a 4gb kit and a 8gb kit for a total of 24gb of ram. It's not ideal but hey, it works.
AFAIK its cheaper to buy more than one stick at a time though, so theres that. Would it really set you back to save up for a 2x kit?
It's not a problem until it is... and you can't tell in advance. DRAM changes all the time. Better processes, higher yields yadda, yadda, yadda and all the manufacturers are sourcing from different suppliers. So even if the RAM has the same specs there's no guarantee that it is identical. They don't warehouse this stuff so any gap in time will give you different production runs. And no one will RMA because of RAM mismatch.
All that said, it IS doubtful there will be too much trouble. Your best bet tho is to buy in pairs, always. So save up and get a 2x16 kit.
Unless the ram is significally more expensive is just stuck in a box and called a kit. Buying more ram down the line is totally fine just buy the same spec ram,
But it's all about production dates. Even just grabbed from the line and put in a box as you said, it's still matched. Same production line, age and quality. Once you get away from that the differences will pile up. And don't be surprised if any particular version is discontinued. I just had to replace my 2 x 8 gb 1866 RAM and it was discontinued. I went from a C9 latency to C10. 3 years old.
And there is memtest. Ive seen it on ubuntu live installs. Spin one up and run memtest for several hours and you mind can be at ease. The new sticks of ram cause them or the old memory to fail tests. Get a refund if that old ram was enough ram for now.