Which RAM and difference?

[Casterina]

I'm in the process of placing an order for the Optimus laptop but what is the difference between the 16GB Kingston SODIMM 1600MHz (2x8GB) and 16GB HyperX Impact SODIMM 1600MHz (2x8GB) which is £5 more?

 

[Oussebon]

You could look it up in detail on the Kingston website (since they make both) but I believe the Impact will have slightly lower latency, which means it's technically faster.

On the one hand the degree to which you'd notice or be able to measure any difference in a task like gaming is very debatable. But on the other hand, for £5 you may decide you might as well get it.

 

[Tony1044]

From the website, HyperX automatically overclocks itself:

"...HyperX® Impact memory boasts the world’s fastest SO-DIMM frequency – 2666MHz – to keep you ahead of the curve and level up your game. It automatically recognises the platform it’s plugged into and auto overclocks to the highest frequency published1 (up to 2400MHz2 ) with no need to adjust system BIOS settings. So you get extreme performance that supports notebooks and other small form factor systems using either AMD or the latest Intel CPU technologies with no hassle at all – even if you’re a newbie..."

(That was the DDR3 blurb)

 

[Oussebon]

and auto overclocks to the highest frequency published

That's just describing XMP I think in a slightly jazzed up way. So 2133MHz DDR4 Impact will still only be 2133MHz, coz' that's the highest published speed

DDR4 2133MHz Impact: http://www.kingston.com/dataSheets/HX421S13IB_8.pdf (CL13)
Each module supports Intel® Extreme Memory Profiles (Intel® XMP) 2.0. This module has been tested to run at DDR4-2133 at a low latency timing of 13-13-13 at 1.2V.

ValueRAM 2133MHz: http://www.kingston.com/dataSheets/KVR21S15S8_8.pdf (CL15)
The SPD is programmed to JEDEC standard latency DDR4-2133 timing of 15-15-15 at 1.2V.