ddr4 2400 memory running at 2133mhz

[silverchairbg]

I've just got this machine and it came with 64GB (4 x 16gb) of Hynix DDR4-2400 ram, which according to the HP specs is what it supports. However the ram is not running at 2400Mhz, rather it's downclocked to 2133mhz. I've looked at bios and could not find any setting that might affect that speed and it also shows the ram is running at 2133mhz in the bios as well. I've found this thread (https://h30434.www3.hp.com/t5/Business-Notebooks/Zbook-15-G6-RAM-speeds/td-p/7589422) which is for the 15 G6 version where it says when 4 dimm slots occupied it would run on slower speeds. However I could not find similar statements for the 17 G4. Any insights?

[Huffer]

The Service Manual clearly says the memory can run at -2400 speed. I have the Zbook 15 G3 with 32 gigs which is its max and all 4 slots are occupied. There was no speed decrease when I populated 2 additional slots. I assume you bought the machine used. Can you tell us the exact type of memory installed? I ask but Hynix should be compatible stock OEM memory. You might try removing 2 modules and see if the memory then runs at -2400. 

[silverchairbg · Accepted solution]

@Huffer Thanks for the reply. I've tried removing 2 modules and voila it now works at 2400Mhz. Although they're exactly the same I've switched them around to make sure they work @2400 by pairs and they do. As soon as I add all 4 of them the speed goes to 2133Mhz however. So yet another HP limitation I guess which isn't documented and was probably included in the G6 quickmanual because of people complaining. Just to be thorough I tested 2666Mhz ram and although it worked it only worked @2400Mhz, so for anyone wondering - this machine would not take advantage of higher speed memory.

P.S. I have 15 G2 as well and not only it works with 32GB of ram at full speed, but it even goes beyond that as I am running 1866Mhz ram on it, when as per documentation it says up to 1600Mhz. So not sure whether HP or Intel dropped the ball, but yeah ..

[TurtleTamer]

Just did a bunch of research on the zbook g3/g4 zbook series, as I am building a super computer with a few of them.

This is what I have discovered about the RAM. 

64gb is supported, however, the memory controller must downclock to handle the additional scan time taken on each read, the physical driver on the board is limited on the voltage at 1.2v, and to support the 64gb the workaround was to downclock the on-board driver. The processor can support 64gb, the board technically can't. 

4 sticks of 8gb runs at 2133 on a g3, and 2400 on a g4 using the exact same Samsung dual rank c17 8gb sticks.

Also.

C17 is the maximum supported style of ram for all 4 slots.

I tried cl18 on a g4, and got the 5 beep memory error with 4 sticks of 2666 kingston fury impact.

Booted fine with two sticks/ but NOT in dual channel mode/ still got beep code.

Also, the two sticks of cl18 in single channel when it did post was at 2400MHz,  therefore, a diminishing return.

TLDR

The optimum setup for the hpZbook g3/g4 is 4 sticks of 8 gb 2400MHz cl17 dual rank memory,

OR

2 sticks of 16gb24000mhz c17 dual rank memory set up in dual channel mode.

Anything else will no post or down clock.

Wanted to leave my findings for any other hackers finally getting their hands on the best bang for buck laptop ever made.