The IBM POWER8 Review: Challenging the Intel Xeon
by Johan De Gelas on November 6, 2015 8:00 AM EST- Posted in
- IT Computing
- CPUs
- Enterprise
- Enterprise CPUs
- IBM
- POWER
- POWER8
The L4-cache and Memory Subsystem
Each POWER8 memory controller has access to four "Custom DIMMs" or CDIMMs. Each CDIMMs is in fact a "Centaur" chip and 40 to 80 DRAM chips. The Centaur chip contains the DDR3 interfaces, the memory management logic and a 16 MB L4-cache.
The 16 MB L4-cache is eDRAM technology like the on-die L3-cache. Let us see how the CDIMMs look in reality.
Considering that 4Gb DRAM chips were available in mid 2013, the 1600 MHz 2Gb DRAM chips used here look a bit outdated. Otherwise the (much) more expensive 64GB CDIMMs use the current 4Gb DRAM chips. The S822L has 16 slots and can thus use up to 1TB (64GB x 16) in DIMMs.
Considering that many Xeon E5 servers are limited to 768 GB, 1 TB is more than competitive. Some Xeon E5 servers can reach 1.5 TB with 64 GB LR-DIMMs but not every server supports this rather expensive memory technology. It is very easy to service the CDIMMs: a gentle push on the two sides will allow you to slide them out. The black pieces of plastic between the CDIMMS are just place-holders that protect the underlying memory slots. For our testing we had CDIMMs installed in 8 of our system's 16 slots.
The Centaur chip acts as a 16MB L4-cache to save memory accesses and thus energy, but it needs quite a bit of power (10-20 W) itself and as a result is covered by heatsink. CDIMMs have ECC enabled (8+1 for ECC) and have also an extra spare DRAM chip. As result, a CDIMM has 10 DRAM chips while offering capacity of 8 chips.
That makes the DRAM subsystem of the S822L much more similar to the E7 memory subsystem with the "Scalable memory interconnect" and "Jordan Creek" memory buffer technology than to the typical Xeon E5 servers.
Facebook
Twitter
RSS
146 Comments
View All Comments
JohanAnandtech - Saturday, November 7, 2015 - link
Ok, Europe adopt the dot, but maybe the US can adopt the metric system like the rest of the world? :-)bitaljus - Saturday, November 7, 2015 - link
or better yet recode this site to see from what country u are visiting and use the appropriate denote thousands symbol, appropriate metric system and even time for the viewer. how meany time i was irradiated when i need to google something like this just to make it in local. and this is easy to do in the site natively. (P.S. Sorry for bad English, not native)nils_ - Wednesday, November 11, 2015 - link
The browser already sends a header with Accept-Language, which should be the preferred way to for the web site to determine locale. For example, I live in Germany so my browser will send en, en_UK, en_US, de and DE (this can be set somewhere in the settings). Now you can determine the language and other localisation based upon that, and there are tools where you can set the locale to then display dates, times etc.. based n that.Many sites instead use Geolocation based on the IP address, which can be really awkward when you travel to a country where you can't read the language.
ZeDestructor - Saturday, November 7, 2015 - link
Even within EU it's not consistent.. UK uses commas for thousands, dot for decimal (and that's why the US and most anglophone countries use the same setup), Germany, Netherlands and France on the other hand favour dots for thousands, commas for decimal, so you see it used there.. and in a great number of their former colonies where the language and culture has stuck.nils_ - Wednesday, November 11, 2015 - link
Dates / Time are even funnier, that's also extremely inconsistent and can be very misleading. Think for examle a date like 12/11/2015, in some countries it'll mean the 12th of November while in others it will mean the 11th of December, and sometimes even the 2015th of November in 11 AD ;)I remember reading on the GTA IV in-game "Internet" a travel guide to Europe that said the months here have 12 days but there are 30 months a year or something to that effect ;)
powchie - Friday, November 6, 2015 - link
let Johan do more reviews. been reading his stuff from late 90's and consider him the best then followed by Anand.Ryan Smith - Saturday, November 7, 2015 - link
Trust me when I say that if I could whip Johan any harder and make him work any faster I would be doing just that.;-)juhatus - Saturday, November 7, 2015 - link
When the Balrog showed up for work he had everyone fired.ruthan - Friday, November 6, 2015 - link
In summary should be something about software support, raw power is here, but software stack isvery limited.
PowerCPU is good for old legacy apps - SAP, Oracle etc.. but otherwise its dead end.
I would like to see comparision of IBM LPAR virtualization against Xeon Vmware solution, or Oracle / MySQL benchmark on power vs. Oracle benchmark on Xeon.
Server with Power even cant to run Crysis, or maybe some QEMU magic..
ruthan - Friday, November 6, 2015 - link
Pleas Ad edit button like other civilized sites, i was hurry when i wrote it.