memory speed hp z800

[dadimi]

hello,

i have a hp z800 (v2) with 2 x5690's, with 6 8gb modules SK hynix HMT31GR7CFR4A-PB (8GB DDR3-1333 RDIMM PC3L-10600R Dual Rank x4 Module). these should run at 1333 according the the memoryguide, but they are only running at 800... 

they are in the black slots in triple channel mode, so everything should be fine, am i missing something here...?

[dadimi]

i also tried 6 modules of 16 gb (samsung m393b2g70qh0-yh9q8 16GB PC3-10600 DDR3-1333MHz ECC Registered CL9 240-Pin DIMM 1.35V Low Voltage Dual Rank Memory Module) and these ran at 667 mhz... 

[DGroves]

Depending on the memory configuration and processor model installed

the memory speed may run at 1866MHz, 1600MHz, 1333MHz, or 1066MHz.

please read the z800 user manual for details

https://h20331.www2.hp.com/Hpsub/downloads/Mini_WP_Z800_memory.pdf

[SDH]

I believe that DGroves, our resident expert on the various 8 series HP workstations, was conflating the Z800 v2 with the Z820 v2 workstations. While it is true that a Z800 v2 can run certain 1866MHz and 1600MHz ECC buffered memory sticks it can only run those to the max speed that a Z800 v2 motherboard can run (1333MHz), and that only can happen if the processor(s) in place also are rated to run at 1333MHz. Plus, there are even other factors that can result in that Z800 v2 workstation not being able to reach 1333MHz full speed, such as the memory's "rank" and also large size of memory stick(s). 

If you do a google search for maximum memory speed in a HP Z800 workstation you'll find some excellent posts from him from the past that go into that in greater detail...

[DGroves]

https://support.hp.com/ie-en/product/hp-z800-workstation/3718645/document/c01709726

[dadimi]

thank you for the answers.

i was wrong about the memory, it's this type of module : HYNIX HMT31GR7CFR4A-PB 8gb (1x8gb) 1600mhz Pc3-12800r Ecc Registered Dual Rank X4 1.35v Ddr3 Sdram 240-pin Rdimm Memory Module For Server. 6 of them, installed following the Mini_WP_Z800_memory.pdf 

I think they meet the specifications listed in this document for them to run at 1333...

it's a dual setup with x5690, these should be ok for 1333 too

i can't test in another machine, so i wonder, did i misinterpret and the modules are simply off-spec for optimal usage with the z800, or do i maybe have another issue... maybe power related? it's not the original hp psu in there, i modded a standard 850w single rail psu into the case with an adapter cable (never had any other issues with powerconsumption though, there is a gtx1070 in it...)

or maybe something wrong with the mobo/memory slots...? I will try other combinations with fewer modules and see if there's any difference

[DGroves]

for a DUAL z800 cpu setup EACH CPU requires 3 dimm modules to be installed

(see the module placement picture in the pdf file i previously linked to)

so if using 4gb dimms the total memory is 24GB using 6 physical modules

cpu-0 slots 1/3/5

cpu-1 slots 1/3/5

the link below shows the HP quickspecs that shows the supported series 56xx models cpu memory speeds

however note that any quad ranked modules will always force the system to 800mhz speeds

https://www.dectrader.com/pdf/quickspecs/13278_na/13278_na.html

[dadimi]

dear Dgroves,

this is exactly how i configured them (1-3-5, 1-3-5, 3 per cpu)

It's like the module's rated speed is divided in half each time...

when i try the 8gb 12800r modules (48gb total), that are 1600 rated they run at 800

and i tried 16 gb 10600 modules (96 total), rated at 1333, they run at 667...

they are all dual rank, ecc and registered, i see no reason why the memory speed is cut in half,

i'm at my wit's end here...

[SDH · Accepted solution]

Your comment brought back a memory of actual vs effective memory chip speeds. After all, DDR stands for Double Data Rate. I took a brief look again at the Wiki section on DDR3 RAM. You may spend more time with it than I was willing to do given your angst, at the link HERE .

What you are reporting may have to do with what you are truly measuring... actual, not effective?

From that link, with my emphasis added in bold:

"DDR3 modules can transfer data at a rate of 800–2133 MT/s using both rising and falling edges of a 400–1066 MHz I/O clock."  "Because the hertz is a measure of cycles per second, and no signal cycles more often than every other transfer, describing the transfer rate in units of MHz is technically incorrect, although very common. It is also misleading because various memory timings are given in units of clock cycles, which are half the speed of data transfers."

[dadimi]

That's it of course...! I as worrying for nothing, cpu-z shows half the speed, didn't know that... So I'm sorry I took up your time with my stupid question... I now have 6x16gb modules (10600) and 6x8gb (12800), and they are all running at 1333mhz, so everything is normal.

Thank you for the feedback and lessons. 

I'm still very happy about the performance of this nearly 15 years old platform, especially now with a m2 nvme ssd (970evo plus) with clover bootloader. Only booting goes very slow