Nehalem - Everything You Need to Know about Intel's New Architecture
by Anand Lal Shimpi on November 3, 2008 1:00 PM EST- Posted in
- CPUs
Integrated Memory Controller
In Nehalem’s un-core lies a number of DDR3 memory controllers, on-die and off of the motherboard - finally. The first incarnation of Nehalem will ship with a triple-channel DDR3 memory controller, meaning that DDR3 DIMMs will have to be installed in sets of three in order to get peak bandwidth. Memory vendors will begin selling Nehalem memory kits with three DIMMs just for this reason. Future versions of Nehalem will ship with only two active controllers, but at the high end and for the server market we’ll have three.
With three DDR3 memory channels, Nehalem will obviously have tons of memory bandwidth, which will help feed its wider and hungrier cores. A side effect of a tremendous increase in memory bandwidth is that Nehalem’s prefetchers can work much more aggressively.
I haven’t talked about Nehalem’s server focus in a couple of pages so here we go again. With Xeon and some server workloads, Core 2’s prefetchers were a bit too aggressive so for many enterprise applications the prefetchers were actually disabled. This mostly happened with applications that had very high bandwidth utilization, where the prefetchers would kick in and actually rob the system of useful memory bandwidth.
With Nehalem the prefetcher aggressiveness can be throttled back if there’s not enough available bandwidth.
QPI
When Intel made the move to an on-die memory controller it needed a high speed interconnect between chips, thus the Quick Path Interconnect (QPI) was born. I’m not sure whether or not QPI or Hyper Transport is a better name for this.
Each QPI link is bi-directional supporting 6.4 GT/s per link. Each link is 2-bytes wide so you get 12.8GB/s of bandwidth per link in each direction, for a total of 25.6GB/s of bandwidth on a single QPI link.
The high end Nehalem processors will have two QPI links while mainstream Nehalem chips will only have one.
The QPI aspect of Nehalem is much like HT with AMD’s processors, now developers need to worry about Intel systems being a NUMA platform. In a multi-socket Nehalem system, each socket will have its own local memory and applications need to ensure that the processor has its data in the memory attached to it rather than memory attached to an adjacent socket.
Here’s one area where AMD having being so much earlier with an IMC and HT really helps Intel. Much of the software work that has been done to take advantage of AMD’s architecture in the server world will now benefit Nehalem.
New Instructions
With Penryn, Intel extended the SSE4 instruction set to SSE4.1 and in Nehalem Intel added a few more instructions which Intel is calling SSE4.2.
The future of Intel’s architectural extensions beyond Nehalem lie in the Advanced Vector Extensions (AVX), which add support for 256-bit vector operations. AVX is an intermediate step between where SSE is today and where Larrabee is going with its instruction set. At some point I suspect we may see some sort of merger between these two ISAs.
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qurious69ss - Friday, August 22, 2008 - link
You sound like one of those sad fanboys from amdzone. Tell dimentia to get a life.X1REME - Friday, August 22, 2008 - link
wow, this whole cpu is a copy of a amd cpu and you expect amd fan boys to not get amd with you, secondly this fantasy is baseless until you can compare it to an offering from the AMD team (Shanghai & Deneb). AMD is still KING with there OPTERON and most likely will be in the future with there new cpu coming soon for the server and also for the desktop.DigitalFreak - Friday, August 22, 2008 - link
Learn to spell, you goober.X1REME - Friday, August 22, 2008 - link
OK DORK, am sure you have never made a mistake (there=their) Duh. I bet your some kid all hyped up for the i7 who wishes Xmas comes early lol. Anyway it’s not a desktop chip, it’s a sever chip DUH. It’s meant to compete with the AMD Opteron chip (the best). Although Opteron will lose its crown, it won’t be to i7 but to Shanghai (AMD new latest and greatest). And like I said b4, Deneb will clear anything up out of place.The reason amd does not grab a microphone and star shouting at the top of their voice is because amd doesn't have the resources and money in comparison with Intel. If it reveals too much about its future strategy and Intel likes that strategy (like the Opteron, HT, On-board mem etc) there is a big theoretical chance that Intel could take this idea and deliver a product well before AMD. So it’s not over until amd says its.
snakeoil - Thursday, August 21, 2008 - link
nehalem fails,it was supposed to be superior to core 2, intel was against the wall this time, why?, because, the old front bus architecture was lagging more more in the server arena and becoming a bottleneck ,compared to hypertransport, so intel is forced to abandon the front side bus, but the strong point of core 2 is that because you don't have and integrated memory controller you can stuff the processor with a huge L2 cache.so, nehalem sucks in gaming,there is no way that the enthusiast is going to pay more for a processor that produce less fps that they actually have.
and the hyperthreading is a risky move, hypertrheading is known por being power hungry, and although produce gains in some applications,some servers applications actually runs slower, so in many cases the old hyperthreading had to be disabled.
nehalem is crippled for the enthusiast,and the regular user.
nuff said.
AssBall - Saturday, August 23, 2008 - link
You musta missed where Anand says several times its not intended for better gaming? It will be significantly faster than Penryn for multithreaded applications. I guess I don't see how this makes it "fail". Maybe in your fantasy world where 90% of the CPU market are "enthusiasts".snakeoil - Saturday, August 23, 2008 - link
enthusiasts drive the market you fruityassUnlimitedInternets36 - Saturday, August 23, 2008 - link
LOL this year Satan err Santa is going to take away your PC because you don't deserve to have one anymore You Jaded nerd.Gasaraki88 - Friday, August 22, 2008 - link
Thanks! I never knew there was a expert on CPU design in the house. I've learn so much from your well researched, tested and thought out comment...pool1892 - Friday, August 22, 2008 - link
first of all the enthusiast market is a very tiny niche, it would not kill intel if you were right.but you are not. the L2 of penryn (and banias) is much more like the nehalem L3 than the nehalem L2. and if you have a single threaded game it now has 8mb at similar latencies, but with a second buffer, the 256k L2, and a MUCH smaller cache miss penalty.
concerning hyperthreading: please read the article first. nehalem switches off what it does not need, powerwise. and about fiftytwo other very vaild arguments.