Memory speed in HP Z600 and HP Z800

[Petoschka]

Hi. I'm a little confused about the memory configuration in the HP Z800. This, like the Z600 uses the Intel 5520 chipset, yet the memory is supposedly throttled to 1066 MHz or even 800 MHz when 16 GB modules are used.

I am currently using a Z600 with 2 x Xeon x5675 processors and 96 GB of memory (6 x 16 GB modules). However, according to CPU-Z and AIDA64, these run at 1333 MHz, so why is the speed throttled in the Z800?

[DGroves]

the answer is quite simple

the z800/600 uses 3 dimm modules per memory bank  unlike most systems that use 2 dimms per bank

the z800 has twice as many dimm sockets (12) with each dimm module placing a small load on the memory buss and this adds up also 16/32gb dimms will have twice as many chips on the dimm as lower capacity chips

this again places a load and practical limit on the dimm traces that connect the memory chips

so HP has told the z800 Bios to lower the memory speed when high capacity dimms and/or many dimm modules are in use

keep in mind that when the z800 was in production high capacity 16/32gb modules were not in wide production and "LR"

load reduced modules did not yet exist

modern current high capacity memory computer systems will use "LR" modules when using 32/64/128gb sizes

https://www.dasher.com/server-memory-rdimm-vs-lrdimm-and-when-to-use-them/

[SDH]

I think that is old news from before there were compatible faster memory modules. It is true that if you run slow memory the processor (which could run faster) will throttle back to the MHz speed of the slow memory.

With newer faster compatible 16GB/stick memory you should be fine. Your X5765 processor(s) can run memory that is rated for up to 1333 MHz. Of interest I found that my version 2 Z600 could run memory from next generation server' (still ECC buffered DDR3) that are rated at 1866MHz. The processor throttled that memory back down to 1333MHz, as expected. But it ran just fine and I'm sure it would run just fine in your Z800 too (given that it must be a v2 also).

By the way, that was with 1866MHz 8GB and also 16GB sticks... I did not mix sticks. A slower stick will throttle all faster sticks present to the slower speed.

I can get you the exact stick info if you need.

[DGroves]

to "SDH"

the z800/z820 systems will indeed drop the memory speeds if large capacity modules are used

this is pre programed into the bios and cannot be overridden

quad rank modules will always run at 800mhz regardless of the dimm size

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

[SDH]

DGroves,

We're tag-teaming on some of these posts...  🙂

I've never built up a Z800 v2 system, and defer to you on that issue of the large capacity sticks. Let me dig out a set of these 16gB sticks and scan them so you can see if I have something that might not cause a ZX00 workstation to slow down with them. It does not make sense to me that they would run at full speed on a Z600 v2 and not a Z800 v2, but stranger things have happened.  If it is dictated by BIOS differences, however, I can see how that could be forced to happen.

I'll get those images posted here tomorrow...

[SDH]

The pictures below show exactly what I used in a Z600 v2 workstation with two of the same processors you have, and they worked fine. Note they are dual rank... maybe that is why they worked so well. DGrove's attached link on Z800 points to quad rank memory being throttled to 800 MHz. 

This is the same memory that also can run fine at full 1866 speed in our Z420 Z620 souped up workstations with single 1866 MHz processor in place for either, usually a E5-1660 v2.  EDIT:  We only have tested with the v2 revision of the ZX00 and ZX20 workstations... never wanted a v1 so never had one to test with.

[DGroves]

while "LR" 32/64gb dimms are now available from most memory makers this was not the case when the z800 was a current system 

the reason HP slows down the  dimm speed is due to the chips using "quad rank"  for the chips on the dimm this setup is like cramming two dual rank dimms into one, and this increases the latency and electrical load on the memory bus along with the actual number of dimm slots (12) on the z800/z820....... it became necessary to lower the memory buss/dimm memory speed in order to maintain system stability as the z800 does not support "LR" dimms

the z820 during it's life as a current system, had later z820 quickspecs list "LR" dimms  for large memory configs

The HP Z800 Workstation maxes out at 192GB of ECC Registered memory (12 x 32GB). Whereas unbuffered tops out at 96GB (12 x 8GB). Depending on the memory configuration and processor model the memory speed may run at 1866MHz, 1600MHz, 1333MHz, or 1066MHz. or 800mhz for quad rank dimms

[SDH]

Good to know... hey, D, does a 16GB dual rank stick like I show in the pics draw less power from the motherboard than a 16GB quad rank stick? I wish I had a Z800 v2 to test with, but we've moved on by several generations now.

However, at home I still am running a souped up Z400 and Z600 just for the fun of it. Surprisingly fast performers with W11 22H2 loaded.

[DGroves]

it's not really a power issue,....... a dual 16gb dimm will draw about the same as a quad rank

what's important is how the dimms memory chip is organized  dual rank in most cases works out best in regards to the load placed on a memory buss by a dimm and the latency of said dimm

https://www.crucial.com/support/articles-faq-memory/what-is-a-memory-rank

i also just parted with my last z800 this year and am now down to two z820's and one z840

while the new "Z" workstations look nice spec wise the pricing is not! which is why my main system is now  AMD ryzen based

[Petoschka]

Maybe I can test it today. Actually, my Z800 should arrive today, but the parcel service "Hermes" is unfortunately very unreliable. My Z600 is equipped with dual rank memory and this should then go into the Z800 together with the CPUs.