I atempted to upgrade the memory in my DL4100 by adding a so-dimm.
WDC Product Page states:
Memory
2 GB DDR3L, expandable to 6 GB max via single SO-DIMM slot unpopulated
Upgradeable with 1x 4 GB DDR3, 1600MHz, CL9, 1.5V, Unbuffered, SODIMM
or with 1x 4 GB DDR3, 1333MHz, CL9, 1.5V, Unbuffered, SODIMM
Not every RAM module works fine with Intel Atom C2350 (DL2100, normal 240-Pin DIMM module ) or C2338 (DL4100, SO-DIMM module) chipset. Actual Intel Atom chipsets are using DDR3L, low-voltage RAM with 1.35 Volt. This is not a problem with SO-DIMMs because most actual laptops need DDR3L RAM too. But 240-pin Standard DIMM modules are mainly 1.5 Volt with no chance to be used in 1.35 Volt slots. WD seems to have tested Kingston RAMs which work.
Best option is to order 1.35 Volt 240-pin RAM modules for the DL2100.
I’ve ordered the Hynix one as it is faster and because I know the chip itself is Made in Korea, which I trust. It was cheaper than Kingston as well. I had a hunch of wanting to order something else, but I just went with what they had recommended and was able to purchase the Hynix for $23 shipped.
Make sure the model number is 100% correct. Double-double check. Do not over look this and order the wrong one. The “L” after the PC3(L) means Low voltage which is what you need. It operates at 1.35 volts…
Traditionally the other rams run at 1.5V…you don’t want 1.5V. Hence, why a lot of people are experiencing problems with errors. I also liked the Hynix over the Kingston because the data transfer rate is 1600MHz, where as the Kingston was only 1333MHz. Hope this helps. Good luck!
When I first got my DL2100 (March 2015) I took the cover off the DL2100 and checked the baseline installed memory after removing the outer case - memory (1GB) is permanently installed on the “mother board” with a slot in the for adding the expansion DIMM.  I can’t get to the backside of the built-in memory without dismantling the device.  The following is what I can see from the opening for the expansion slot:
there are eight (8) chips with the following printed on each chip:Â
NANYA 1445
WT5CC128M8FN-D1
434349WQEF 3 TW
I sent this data to Data Memory Systems (DMS) customer service and they provided the following:Â
FYI, there is a WD FAQ online here telling which memory boards to install in the EX and DL series. I put the recommended Kingston in my DL2100 and it works great and costs around $25 from Amazon. I see I have that info bookmarked, so here is the link:
I bought this one for my DL2100 from Amazon for a good price I believe it is the first one on the WD list, the faster one of the two, and the more recent model of card with higher specs. CL in the description designates, I believe is the L you are asking about. I explored each of the two cards at Kingston site. This is the one to get. (The older model was an alternative selection in case this one could not be located, but there it is at Amazon.)
CL11 is related to the latency. not the same thing as ddr3L
what was confusing was that they say on that FAQ page that dl2100 has ddr3L ram (1,35V) and also on the data sheet (upgradable with ddr3L) but then their recommendation and approved ram is to use kingston ddr3 (1,5V) ram chips.
Yea, thanks for reminding me of that. No matter, the memory card you ordered is gonna work fine. If I remember, there are 4 screws near bottom of unit. take them out and the outer case either lifts up or unit slides out. Either way, you can figure it out. Memory slot is in a open compartment at top of unit.