Further Power Managed Cache?

One new thing we learned about Nehalem at IDF was that Intel actually moved to a 8T (8 transistor) SRAM cell design for all of the core cache memory (L1 and L2 caches, but not L3 cache). By moving to a 8T design Intel was able to actually reduce the operating voltage of Nehalem, which in turn reduces power consumption. You may remember that Intel’s Atom team did something similar with its L1 cache:

“Instead of bumping up the voltage and sticking with a small signal array, Intel switched to a register file (1 read/1 write port). The cache now had a larger cell size (8 transistors per cell) which increased the area and footprint of the L1 instruction and data caches. The Atom floorplan had issues accommodating the larger sizes so the data cache had to be cut down from 32KB to 24KB in favor of the power benefits. We wondered why Atom had an asymmetrical L1 data and instruction cache (24KB and 32KB respectively, instead of 32KB/32KB) and it turns out that the cause was voltage.

A small signal array design based on a 6T cell has a certain minimum operating voltage, in other words it can retain state until a certain Vmin. In the L2 cache, Intel was able to use a 6T signal array design since it had inline ECC. There were other design decisions at work that prevented Intel from equipping the L1 cache with inline ECC, so the architects needed to go to a larger cell size in order to keep the operating voltage low.”

Intel states that Nehalem’s “Core memory converted from 6-T traditional SRAM to 8-T SRAM”. The only memory in the “core” of Nehalem is its L1 and L2 caches, which may help explain why the L2 cache per core is a very small 256KB. It would be costly to increase the transistor count of Nehalem’s 8MB L3 cache by 33%, but it’s also most likely not as necessary since the L3 cache and the rest of the uncore runs on its own voltage plane as I’ll get to shortly.

Cache Hierarchy Integrated Memory Controller
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  • niva - Friday, August 22, 2008 - link

    Well it is another step forward for Intel while AMD is still falling farther and farther behind the times. I want to caution that at this point there is no software actually optimized to run on i7 and any potential new instructions the chips will have. Once that happens and games are patched/recompiled or new games come out to take advantage of the massive CPU/memory bandwidth i7 offers it will be lights out.

    Waiting on AMD to come out with the next best thing is becoming really old. I have a Phenom system, I won't need a new one for at least another year or two but even though I wish AMD would do better they're just being dominated by intel right now.
    Reply
  • qurious69ss - Friday, August 22, 2008 - link

    You sound like one of those sad fanboys from amdzone. Tell dimentia to get a life. Reply
  • 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. Reply
  • DigitalFreak - Friday, August 22, 2008 - link

    Learn to spell, you goober. Reply
  • 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.
    Reply
  • 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.
    Reply
  • 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".

    Reply
  • snakeoil - Saturday, August 23, 2008 - link

    enthusiasts drive the market you fruityass Reply
  • UnlimitedInternets36 - 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. Reply
  • 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... Reply

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