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Intel Core i7 (Nehalem): Architecture By AMD?

Branch Predictors

The last improvement to the front end has to do with the branch predictors. The efficiency of branch prediction algorithms becomes crucial in architectures that need high levels of instruction parallelism. A branch breaks the parallelism because it necessitates waiting for the result of a preceding instruction before execution of the flow of instructions can be continued. Branch prediction determines whether or not a branch will be taken, and if it is, quickly determines the target address for continuing execution. No complicated techniques are needed to do this; all that’s needed is an array of branches—the Branch Target Buffer (BTB)—that stores the results of the branches as execution progresses (Taken or Not Taken and target address) and an algorithm for determining the result of the next branch.

Intel hasn’t provided details on the algorithm used for their new predictors, but it is known that they are now two-level predictors. the first level is unchanged from the Conroe architecture, but a new level with slower access that can store more branch history has been added. According to Intel, this configuration improves branch prediction for certain applications that use large volumes of code, such as databases—more evidence of Nehalem’s server orientation. Another improvement is to the Return Stack Buffer, which stores the return addresses of functions when they’re called. In certain cases this buffer can overflow, which could lead to faulty predictions. To limit that possibility, AMD increased its size to 24 entries, whereas with the Nehalem Intel has introduced a renaming system for this buffer.

  • cl_spdhax1
    good write-up, cant wait for the new architecture , plus the "older" chips are going to become cheaper/affordable. big plus.
    Reply
  • neiroatopelcc
    No explaination as to why you can't use performance modules with higher voltage though.
    Reply
  • neiroatopelcc
    AuDioFreaK39TomsHardware is just now getting around to posting this?Not to mention it being almost a direct copy/paste from other articles I've seen written about Nehalem architecture.I regard being late as a quality seal really. No point being first, if your info is only as credible as stuff on inquirer. Better be last, but be sure what you write is correct.
    Reply
  • cangelini
    AuDioFreaK39TomsHardware is just now getting around to posting this?Not to mention it being almost a direct copy/paste from other articles I've seen written about Nehalem architecture.
    Perhaps, if you count being translated from French.
    Reply
  • randomizer
    Yea, 13 pages is quite alot to translate. You could always use google translation if you want it done fast :kaola:
    Reply
  • Duncan NZ
    Speaking of french... That link on page 3 goes to a French article that I found fascinating... Would be even better if there was an English version though, cause then I could actually read it. Any chance of that?

    Nice article, good depth, well written
    Reply
  • neiroatopelcc
    randomizerYea, 13 pages is quite alot to translate. You could always use google translation if you want it done fast I don't know french, so no idea if it actually works. But I've tried from english to germany and danish, and viseversa. Also tried from danish to german, and the result is always the same - it's incomplete, and anything that is slighty technical in nature won't be translated properly. In short - want it done right, do it yourself.
    Reply
  • neiroatopelcc
    I don't think cangelini meant to say, that no other english articles on the subject exist.
    You claimed the article on toms was a copy paste from another article. He merely stated that the article here was based on a french version.
    Reply
  • enewmen
    Good article.
    I actually read the whole thing.
    I just don't get TLP when RAM is cheap and the Nehalem/Vista can address 128gigs. Anyway, things have changed a lot since running Win NT with 16megs RAM and constant memory swapping.
    Reply
  • cangelini
    I can't speak for the author, but I imagine neiro's guess is fairly accurate. Written in French, translated to English, and then edited--I'm fairly confident they're different stories ;)
    Reply