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Does Additional RAM Need to be same MHz, CL, etc as Existing RAM?
01-23-2016, 10:11 AM, (This post was last modified: 01-23-2016, 10:17 AM by Alan_Schezar.)
Question  Does Additional RAM Need to be same MHz, CL, etc as Existing RAM?

I am attempting to increase my DDR4 RAM from 8GB to 24GB. My Alienware Area-51 X99 computer came with 2x4GB, and I am looking to fill the 2 remaining DIMM slots with a 2x8GB increase.

My current DDR4 RAM is 2133 MHz, CL15. Does the new RAM need to be the same MHz and CL?

The current DDR4 suggestions for best PC Parts have a higher MHz (2400) and CL (16).

Here is a link to exactly what I have:

- Samsung M378A5143DB0-CPB DDR4-2133 4GB/512Mx8 CL15 Desktop Memory Bulk OEM

Here are the links to the RAM that I am considering:

- Crucial 16GB Kit (8GBx2) DDR4 2133 MT/s (PC4-17000) CL15 DR x8 Non-ECC UDIMM 288-Pin Memory CT2K8G4DFD8213/CT2C8G4DFD8213

- Crucial Ballistix Sport 16GB Kit (8GBx2) DDR4 2400 MT/s (PC4-19200) DIMM 288-Pin Memory BLS2K8G4D240FSA/BLS2C8G4D240FSA

Thanks again!Cool
01-23-2016, 03:00 PM, (This post was last modified: 01-23-2016, 03:01 PM by Dan-H.)
RE: Does Additional RAM Need to be same MHz, CL, etc as Existing RAM?
Dell systems I've owned cannot change memory speed or timings in BIOS so if the Alienware is similar you may be stuck with whatever speed the BIOS auto detects.

Unless the BIOS allows you to set the speed of the memory I'd want to match speed and latency of the new memory with the old and then test to make sure you are getting the same performance.

I installed a mis-matched set of memory in one of my i7 4770-Z87 Dell desktops, and it downclocked all the memory to 1333Mhz CL9 even though one set was 1600Mhz CL9 and the other 1600Mhz CL7. (edit: 2x4GB CL9 plus 2x8GB CL7)

Consider installing Intel XTU and record the subtimings before and after. Or better still, check current timings with XTU (take a screen shot) , remove the two 4G sticks, install the two 8G sticks, check timings again then install all of the memory and check them again and see if they remain the same.

I'd run memory focused benchmarks before and after to make sure the speed is not slower with the additional memory.

Disclaimer: I have zero DDR4 experience and no idea what that the Alienware BIOS will let you set. My comments are more general and not specific at all to that system.
CPU: Intel Core i7-4790K 4.7Ghz Mobo: Gigabyte Z97X Gaming 5 GPU: MSI GTX 970 Gaming 4G HSF: Cryorig R1 Ultimate
Mem: 2 x 8GB G.Skill TridentX DDR3 2400 SSD: Samsung 850 Evo 500GB + a few spinners
PSU: Seasonic SS-760XP Platinum Case: Fractal Design Define R5 Monitors: 2 x Dell 2007FP 1600x1200

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