Previously I’ve mentioned the followings regarding the latest DDR3L RAM:

It’s nice to have that 20% electricity saving, but when you add 2DPC (2 DIMMs Per Channel), your nice 20% power saving (ie, 1.35V) will be disabled automatically (ie, raise to 1.5V instead). However the good part is you still get that 1333Mhz bandwidth with 2DPC. DDR3L 1.35V will only apply when it’s in 1DPC mode.

What I’ve found out today during the server upgrade is the above may not be always true.

May be it’s related to the Poweredge BIOS that I’ve updated sometimes ago as it may contain the changes now allowing 2DPC operating at 1.35V Low Voltage. (may be even 3DPC)

The server is Poweredge R610 with 1 CPU Xeon E5620 (32nm, 12M Cache, 2.40 GHz, 5.86 GT/s, max supports DDR3-1066). After I filled up all the available 6 DIMMS, (ie, 3 Channels, 2 DIMMS per channel), I saw during the rebooting screen, it showed DDR- 1066Mhz and 1.35V, This is Great! I was expecting to see 1.5V as this happens to my R710 when putting 2DPC, it automatically raised to 1.5V, probably will go down to 1.35v if I upgraded the BIOS for that R710.

Finally, I located this interesting White Paper about Samsung’s DDR3L RAM, the result shows even with 3DPC at 1.5V, you can still save up to 50% of the total power consumption by using DDR3 Low Voltage RAM. There are also many other interesting technical insides regarding the benefits using DDR3L RAM.

The other thing is the RAM Upgrade KIT somehow did’t come with Heatsink, strange.

What you are seeing in the above picture is a direct comparision of two ALMOST IDENTICAL 4GB RAM, even the IC chipset part number is almost identical except a single character difference. 

The one on top is used in Desktop (Optiplex 990 SSF), I bought it in a local computer shop for under USD20, and the other is for this server upgrade (ie, Poweredge R610).

As you can see there are two extra chips in server ram (hence ECC and Buffer), and note the “L” indicates this server RAM is a Low Voltage version.

I also noticed the desktop ram label says it’s 10600U and server one says 10600R, ha…here is the fun part, I am sure this means U-DIMM (as Un-Buffered) and R-DIMM (as Registered & Buffered), so what does it mean or why this is so important?

Well, technically you can fit a cheap U-DIMM (about USD20 per 4GB DIMM)  into any Poweredge R2xx, R6xx, R7xx, R8xx, R9xx, of course, there is a limit when using U-DIMM, maximum you can use is 24GB, so that’s about 6 DIMMS x 4GB U-DIMM.

And the saving is Huge, for some may be (as USD120 for U-DIMM vs USD420 for R-DIMM), that’s USD20 for a 4GB U-DIMM that you can buy from any local computer shop as they are simply a desktop RAM, comparing to USD70 for the equivalent R-DIMM.

Of course, I will still choose R-DIMM, you may ask for maximum 24GB, why pay that extra  USD300-315 for ECC Reg RAM?  Well…RAS and reliability is the number  one factor in data center business, and not to mention the expandability, so Why NOT?