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Why 64 bit?
Why 64 bit?
Posted Sep 13, 2006 17:29 UTC (Wed) by zlynx (subscriber, #2285)In reply to: Why 64 bit? by charris
Parent article: What you should (and shouldn't) expect from 64-bit Linux (Linux.com)
Now, this may not be factual, but I have read that Intel cheated a bit with EMT-64 instructions.
What they apparently do is run 64-bit operations through their existing 32-bit ALU, and because their P4 architecture has a double-clocked ALU, this isn't so bad. What it does mean though, is that you've just exchanged the instructions a 32-bit compiler generates for 64-bit ops with CPU microcode doing the same thing.
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Why 64 bit?
Posted Sep 14, 2006 6:57 UTC (Thu) by khim (subscriber, #9252) [Link]
It's not the same thing. 64-bit instructions were discowered in the photo of Prescott CPU two years before Intel said that he'll support EM64T! How ? On the photo you can find TWO 32bit ALUs! One is used for 32bit, another one - for high half of the 64bit (it's smaller, it's registers don't have tags so can not be used separately, etc). It means that while it's slower then AMD64 it's still faster then what the compiler does - because the compiler can only use first ALU!