Question about RAM compatibility: P157SM

I've encountered an application (running multiple virtual machines simultaneously) which requires more RAM than is currently installed in my Clevo P157SM (Sager NP8255-S), and so I need to add memory to the system.

The system is currently configured with 8 GB (2x4 GB) of DDR3 1600 MHz CL11 memory installed beneath the keyboard. The slots beneath the bottom cover are open.

Will there be any problems if I add 16 GB (2x8 GB) of DDR3 1600 MHz CL10 memory ( this item) for a total of 24 GB? Note the difference in module density and CAS latency.

I assume the system will read and accept the 24 GB without issues, and all modules will run at 1600 MHz CL11. Can I be sure about this?

--DragonLord

 

You will want to stick with the same CL RAM to avoid any read/write errors. If you're looking for the lower CL I would replace the stock RAM so it all matches. The one you linked is 1.5v, Haswell CPU's use low voltage so you'll want to find 1.35v.

 

DO NOT use 1.5v sticks on Haswell laptops unless you want to play the silicon lottery. Use only 1.35v ram! I highly recommend Kingston's HyperX LoVo ram.

 

CPU-Z says currently-installed memory modules are 1.5V, and the SO-DIMM slots are themselves marked 1.5V. This was actually a bit of a surprise to me as I myself expected the system to take DDR3L 1.35V modules.

The reason I'm looking at the CL10 part rather than the CL11 part is reliability--the CL11 modules seem to have more issues than the CL10 modules.

--DragonLord

 

Perhaps this would be the right part? Newegg.com - G.SKILL 16GB (2 x 8G) 204-Pin DDR3 SO-DIMM DDR3 1600 (PC3 12800) Laptop Memory Model F3-1600C11D-16GSL

2x8 GB DDR3L-1600, CL11.

This makes sense now. The official Clevo documentation calls specifically for DDR3L-1600. I suspect two reasons for the incorrect voltage markings:

• The CPU-Z software simply lists the JEDEC ratings for valid module types, and not the actual voltage of the memory modules.
• DDR3 SO-DIMM modules and slots are not keyed to distinguish between 1.5V DDR3 and 1.35V DDR3L modules; hence, a slot marked for "1.5V" will physically accept a 1.35V DDR3L module.

--DragonLord

 

Yes the slots are marked 1.5v, but they only supply 1.35v. If you run 1.5v sticks at 1600 most of the time they'll work just fine, unless you get really unlucky.

Those GSkill sticks should work just fine.

 

The distinction between DDR3 and DDR3L is a common point of confusion among people working with Haswell systems, and it turns out I was misled by incorrect information.

One last question remains, though: will there be any problems with this 2x8GB+2x4GB configuration? I don't think so, but I just want to double-check. For some odd reason, Sager ships the factory 24 GB configuration as 3x8GB, which does not allow dual-channel operation. This stands in contrast to how others implement memory configurations that are a multiple of 3 on dual-channel systems: on older Dell systems, I've seen 3 GB configured as 2x1GB+2x512MB, and 6 GB as 2x2GB+2x1GB.

--DragonLord

 

You can mix the size of RAM and wont have any problems so your 2x8GB + 2x4GB will work fine.

 

Just ordered the memory. Thanks for the guidance!

--DragonLord

 

Just make sure the ram is matched in each set of slots. So 8gb and 8gb under the keyboard and 4GB +4GB under the service hatch.

 

2x4GB will be under the keyboard, and 2x8GB will be under the bottom cover.

--DragonLord

 

All good then, otherwise a third of the ram would be single channel.