S is for SO-DIMM, the trype of DRAM laptops use
So, it just means that it's 204-pin SO-DIMM memory. Thank you.
Is it a problem if the latencies etc. differs from the stock memory? Both are PC3-12800 but not sure for the other things. The manufacturer is different surely. The voltage should be same but not sure again, will check when I get the laptop.
My reading and understanding of CL's (Cass Latency) is that the lower the number, the lower the delay time for clearing a registry in operations. You may notice that slower (lower frequency) RAM modules tend to have lower latency numbers. High latency numbers are bad but, as long as the frequency is high, (like the 12800 @ 1600GHz), it more than makes up for the CL delay. Again, according to my understanding of it, the RAM modules are controllable and have backwards compatibility with slower modules, (because they can be instructed to operate at both slower speeds (frequencies) within their class (DDR, DDR2, DDR3, and DDR4), and at the higher latency rates as well. So, while faster frequency and lower latency is preferable, mixing these will not be fatal; the faster module will just run at the slower speed and higher latency in maintaining compatibility. I could be wrong but, I believe the lowest Cass Latency for DDR3 ram is CL9 (9-9-9-27).
I currently have a pair of DDR3L-12800s modules in my Lenovo IdeaPad 586. They replace a 4GB module and an 8GB that came with the used laptop when I bought it. The 8 & 4 gigabyte modules didn't have the "s" at the end of the frequency rating. So, while I don't know what the "s" signifies, I am pretty sure it will not cause a problem for your laptop in using it.
I'm pretty sure the 1Rx8 can't be used with a 2Rx8 though. My Acer could use either type, just not together. (I think it has to do with the "density" of the memory registries on the RAM module's PCB wafers.) Some memory modules only have 4 memory blocks on one side of a wafer and the other will have 4 on each side, (8 registry blocks total, with the same number of gigs on them: e.g., 4GB sticks.)